SUMMARY PROSPECTUSLord Abbett Short Duration Income FundAPRIL 1, 2021CLASS A.CLASS C.CLASS F .CLASS F3 .LALDXLDLAXLDLFXLOLDXCLASS/TICKERCLASS I. LLDYXCLASS P. N/ACLASS R2 . LDLQXCLASS R3 . LDLRXCLASS R4. LDLKXCLASS R5. LDLTXCLASS R6. LDLVXBefore you invest, you may want to review the Fund’s prospectus and statement of additionalinformation, which contain more information about the Fund and its risks. You can find theFund’s prospectus, statement of additional information and other information about the Fund You can also get this information at no cost bycalling 888-522-2388 (Option #2) or by sending an email request to [email protected] current prospectus and statement of additional information dated April 1, 2021 as may besupplemented from time to time, are incorporated by reference into this summary prospectus.

INVESTMENT OBJECTIVEThe Fund’s investment objective is to seek a high level of income consistent withpreservation of capital.FEES AND EXPENSESThis table describes the fees and expenses that you may pay if you buy, hold, andsell shares of the Fund. You may pay other fees, such as brokerage commissions andother fees to financial intermediaries, which are not reflected in the tables andexamples below. You may qualify for sales charge discounts if you and certainmembers of your family invest, or agree to invest in the future, at least 100,000 inthe Lord Abbett Family of Funds. More information about these and other discountsis available from your financial intermediary and in “Sales Charge Reductions andWaivers” on page 317 of the prospectus, Appendix A to the prospectus, titled“Intermediary-Specific Sales Charge Reductions and Waivers,” and “Purchases,Redemptions, Pricing, and Payments to Dealers” on page 9-1 of Part II of thestatement of additional information (“SAI”).Shareholder Fees(1) (Fees paid directly from your investment)ClassACF, F3, I, P, R2, R3, R4, R5, and R6Maximum Sales Charge (Load) Imposed on Purchases(as a percentage of offering price)2.25%NoneNoneMaximum Deferred Sales Charge (Load)(as a percentage of offering price or redemptionproceeds, whichever is lower)None(2)1.00% (3)NoneAnnual Fund Operating Expenses(Expenses that you pay each year as a percentage of the value of your investment)ClassACFF3IPManagement Fees0.25%0.25%0.25%0.25%0.25%0.25%Distribution and Service (12b-1) Fees0.20%0.85% (4)0.10%NoneNone0.45%Other Expenses0.14%0.14%0.14%0.07%0.14%0.14%Total Annual Fund Operating Expenses0.59%1.24%0.49%0.32%0.39%0.84%SUMMARY – SHORT DURATION INCOME FUND2

Annual Fund Operating Expenses (continued)(Expenses that you pay each year as a percentage of the value of your investment)ClassR2R3R4R5R60.25%Management Fees0.25%0.25%0.25%0.25%Distribution and Service (12b-1) Fees0.60%0.50%0.25%NoneNoneOther Expenses0.14%0.14%0.14%0.14%0.07%Total Annual Fund Operating Expenses0.99%0.89%0.64%0.39%0.32%(1)A shareholder transacting in share classes without a front-end sales charge may be required to pay a commission to itsfinancial intermediary. Please contact your financial intermediary for more information about whether such a commissionmay apply to your transaction.(2)A contingent deferred sales charge (“CDSC”) of 1.00% may be assessed on certain Class A shares purchased oracquired without a sales charge if they are redeemed before the first day of the month of the one-year anniversary of thepurchase.(3)A CDSC of 1.00% may be assessed on Class C shares if they are redeemed before the first anniversary of theirpurchase.(4)The 12b-1 fee the Fund will pay on Class C shares will be a blended rate calculated based on (i) 1.00% of the Fund’saverage daily net assets attributable to shares held for less than one year and (ii) 0.80% of the Fund’s average daily netassets attributable to shares held for one year or more. All Class C shareholders of the Fund will bear 12b-1 fees at thesame rate.ExampleThis Example is intended to help you compare the cost of investing in the Fund withthe cost of investing in other mutual funds. The Example assumes that you invest 10,000 in the Fund for the time periods indicated and then redeem all of your sharesat the end of those periods. The Example also assumes that your investment has a5% return each year and that the Fund’s operating expenses remain the same. ClassC shares automatically convert to Class A shares after eight years. The expenseexample for Class C shares for the ten-year period reflects the conversion to Class Ashares. Although your actual costs may be higher or lower, based on theseassumptions your costs would be:ClassIf Shares Are RedeemedIf Shares Are Not Redeemed1 Year3 Years5 Years10 Years1 YearClass A Shares 284 410 547 3 Years5 Years946 284 410 54710 YearsClass C Shares 226 393 681 1,320 126 393 681 1,320Class F Shares 50 157 274 616 50 157 274 616Class F3 Shares 33 103 180 406 33 103 180 406493946Class I Shares 40 125 219 493 40 125 219 Class P Shares 86 268 466 1,037 86 268 466 1,037Class R2 Shares 101 315 547 1,213 101 315 547 1,213Class R3 Shares 91 284 493 1,096 91 284 493 1,096Class R4 Shares 65 205 357 798 65 205 357 798Class R5 Shares 40 125 219 493 40 125 219 493Class R6 Shares 33 103 180 406 33 103 180 406SUMMARY – SHORT DURATION INCOME FUND3

Portfolio Turnover. The Fund pays transaction costs, such as commissions, when itbuys and sells securities (or “turns over” its portfolio). A higher portfolio turnoverrate may indicate higher transaction costs and may result in higher taxes when Fundshares are held in a taxable account. These costs, which are not reflected in theannual fund operating expenses or in the example, affect the Fund’s performance.During the most recent fiscal year, the Fund’s portfolio turnover rate was 102% ofthe average value of its portfolio.PRINCIPAL INVESTMENT STRATEGIESThe Fund invests in various types of short duration debt (or fixed income) securities.Under normal conditions, the Fund pursues its investment objective by investing atleast 65% of its net assets in investment grade debt securities of various types. Suchinvestments include: corporate debt securities of U.S. issuers; corporate debt securities of non-U.S. (including emerging market) issuers thatare denominated in U.S. dollars; mortgage-backed, mortgage-related, and other asset-backed securities, includingprivately issued mortgage-related securities and commercial mortgage-backedsecurities (“CMBS”); securities issued or guaranteed by the U.S. Government, its agencies andinstrumentalities; and inflation-linked investments.The Fund may invest in Treasury Inflation Protected Securities (“TIPS”), which areU.S. Government bonds whose principal automatically is adjusted for inflation asmeasured by the Consumer Price Index for All Urban Consumers (“CPI-U”), andother inflation-indexed securities issued by the U.S. Department of Treasury.The Fund may invest up to 35% of its net assets in any one or a combination of thefollowing types of fixed income securities and other instruments: high-yield debt securities (commonly referred to as “lower-rated” or “junk”bonds); debt securities of non-U.S. (including emerging market) issuers that aredenominated in foreign currencies; loans, including bridge loans, novations, assignments, and participations; convertible securities, including convertible bonds and preferred stocks; and structured securities and other hybrid instruments, including collateralized loanobligations ("CLOs").The Fund will not invest more than 25% of its total assets in any industry; however,this limitation does not apply to mortgage-backed securities, privately issuedSUMMARY – SHORT DURATION INCOME FUND4

mortgage-related securities, or securities issued by the U.S. Government, its agenciesand instrumentalities. The Fund may, and typically does, invest substantially inCMBS, including lower-rated CMBS.The Fund seeks to manage interest rate risk through its management of the averageduration of the securities it holds in its portfolio. Under normal conditions, the Fundwill maintain its average dollar-weighted duration range between one and threeyears. The duration of a security takes into account the pattern of all expectedpayments of interest and principal on the security over time, including how thesepayments are affected by changes in interest rates.The Fund may use derivatives to hedge against risk or to gain investment exposure.Currently, the Fund expects to invest in derivatives consisting principally of futures,forwards, options, and swaps. The Fund may use derivatives to seek to enhancereturns, to attempt to hedge some of its investment risk, to manage portfolioduration, as a substitute for holding the underlying asset on which the derivativeinstrument is based, or for cash management purposes. For example, the Fund mayinvest in or sell short U.S. Treasury futures, securities index futures, other futures,and/or currency forwards to adjust the Fund’s exposure to the direction of interestrates, or for other portfolio management reasons.The portfolio management team buys and sells securities using a relative valueoriented investment process, meaning the portfolio management team generallyseeks more investment exposure to securities believed to be undervalued and lessinvestment exposure to securities believed to be overvalued. The portfoliomanagement team combines top-down and bottom-up analysis to construct itsportfolio, using a blend of quantitative and fundamental research. As part of its topdown analysis, the portfolio management team evaluates global economicconditions, including monetary, fiscal, and regulatory policy, as well as the politicaland geopolitical environment, in order to identify and assess opportunities and risksacross different segments of the fixed income market. The portfolio managementteam employs bottom-up analysis to identify and select securities for investment bythe Fund based on in-depth company, industry, and market research and analysis.The portfolio management team may actively rotate sector exposure based on itsassessment of relative value. The investment team may also consider the risks andreturn potential presented by environmental, social, and governance (ESG) factors ininvestment decisions. The Fund may engage in active and frequent trading of itsportfolio securities.The Fund may sell a security when the Fund believes the security is less likely tobenefit from the current market and economic environment, or shows signs ofdeteriorating fundamentals, among other reasons. The Fund may deviate from theinvestment strategy described above for temporary defensive purposes. The Fundmay miss certain investment opportunities if defensive strategies are used and thusmay not achieve its investment objective.SUMMARY – SHORT DURATION INCOME FUND5

PRINCIPAL RISKSAs with any investment in a mutual fund, investing in the Fund involves risk,including the risk that you may receive little or no return on your investment. Whenyou redeem your shares, they may be worth more or less than what you paid forthem, which means that you may lose a portion or all of the money you invested inthe Fund. The principal risks of investing in the Fund, which could adversely affectits performance, include: Portfolio Management Risk: If the strategies used and investments selected bythe Fund’s portfolio management team fail to produce the intended result, theFund may suffer losses or underperform other funds with the same investmentobjective or strategies, even in a favorable market. Market Risk: The market values of securities will fluctuate, sometimes sharplyand unpredictably, based on overall economic conditions, governmental actionsor intervention, market disruptions caused by trade disputes or other factors,political developments, and other factors. Prices of equity securities tend to riseand fall more dramatically than those of debt securities. Fixed Income Securities Risk: The Fund is subject to the general risks andconsiderations associated with investing in debt securities, including the riskthat issuers will fail to make timely payments of principal or interest or defaultaltogether. Lower-rated securities in which the Fund may invest may be morevolatile and may decline more in price in response to negative issuerdevelopments or general economic news than higher rated securities. Inaddition, as interest rates rise, the Fund’s investments typically will lose value. Foreign Currency Risk: Investments in securities denominated in foreigncurrencies are subject to the risk that those currencies will decline in valuerelative to the U.S. dollar, or, in the case of hedged positions, that the U.S.dollar will decline in value relative to the currency being hedged. Foreigncurrency exchange rates may fluctuate significantly over short periods of time. High Yield Securities Risk: High yield securities (commonly referred to as“junk” bonds) typically pay a higher yield than investment grade securities, butmay have greater price fluctuations and have a higher risk of default thaninvestment grade securities. The market for high yield securities may be lessliquid due to such factors as interest rate sensitivity, negative perceptions of thejunk bond markets generally, and less secondary market liquidity. This maymake such securities more difficult to sell at an acceptable price, especiallyduring periods of financial distress, increased market volatility, or significantmarket decline. Credit Risk: Debt securities are subject to the risk that the issuer or guarantorof a security may not make interest and principal payments as they become dueor may default altogether. In addition, if the market perceives a deterioration inthe creditworthiness of an issuer, the value and liquidity of securities issued bySUMMARY – SHORT DURATION INCOME FUND6

that issuer may decline. To the extent that the Fund holds below investmentgrade securities, these risks may be heightened. Insured debt securities have thecredit risk of the insurer in addition to the credit risk of the underlyinginvestment being insured. Interest Rate Risk: As interest rates rise, prices of bonds (including tax-exemptbonds) generally fall, typically causing the Fund’s investments to lose value.Additionally, rising interest rates or lack of market participants may lead todecreased liquidity in fixed income markets. Interest rate changes generallyhave a more pronounced effect on the market value of fixed-rate instruments,such as corporate bonds, than they have on floating rate instruments, andtypically have a greater effect on the price of fixed income securities with longerdurations. A wide variety of market factors can cause interest rates to rise,including central bank monetary policy, rising inflation, and changes in generaleconomic conditions. To the extent the Fund invests in floating rate instruments,changes in short-term market interest rates may affect the yield on thoseinvestments. If short-term market interest rates fall, the yield on the Fund’sshares will also fall. Conversely, when short-term market interest rates rise,because of the lag between changes in such short- term rates and the resetting ofthe floating rates on the floating rate debt in the Fund’s portfolio, the impact ofrising rates may be delayed. To the extent the Fund invests in fixed rateinstruments, fluctuations in the market price of such investments may not affectinterest income derived from those instruments, but may nonetheless affect theFund’s NAV, especially if the instrument has a longer maturity. Substantialincreases in interest rates may cause an increase in issuer defaults, as issuersmay lack resources to meet higher debt service requirements. In recent years, theU.S. has experienced historically low interest rates, increasing the exposure ofbond investors to the risks associated with rising interest rates. Liquidity/Redemption Risk: The Fund may lose money when selling securitiesat inopportune times to fulfill shareholder redemption requests. The risk of lossmay increase depending on the size and frequency of redemption requests,whether the redemption requests occur in times of overall market turmoil ordeclining prices, and whether the securities the Fund intends to sell havedecreased in value or are illiquid. The Fund may be less able to sell illiquidsecurities at its desired time or price. It may be more difficult for the Fund tovalue its investments in illiquid securities than more liquid securities. Government Securities Risk: The Fund invests in securities issued orguaranteed by the U.S. Government or its agencies and instrumentalities (suchas the Government National Mortgage Association (“Ginnie Mae”), the FederalNational Mortgage Association (“Fannie Mae”), or the Federal Home LoanMortgage Corporation (“Freddie Mac”)). Unlike Ginnie Mae securities,securities issued or guaranteed by U.S. Government-related organizations, suchas Fannie Mae and Freddie Mac, are not backed by the full faith and credit ofthe U.S. Government and no assurance can be given that the U.S. Governmentwould provide financial support.SUMMARY – SHORT DURATION INCOME FUND7

Mortgage-Related and Other Asset-Backed Securities Risk: Mortgagerelated securities, including commercial mortgage-backed securities and otherprivately issued mortgage-related securities, and other asset-backed securitiesmay be particularly sensitive to changes in prevailing interest rates andeconomic conditions, including delinquencies and defaults. The prices ofmortgage-related and other asset-backed securities, depending on their structureand the rate of payments, can be volatile. They are subject to prepayment risk(higher than expected prepayment rates of mortgage obligations due to a fall inmarket interest rates) and extension risk (lower than expected prepayment ratesof mortgage obligations due to a rise in market interest rates). These risksincrease the Fund’s overall interest rate risk. Some mortgage-related securitiesreceive government or private support, but there is no assurance that suchsupport will remain in place. Commercial Mortgage-Backed Securities Risk: Commercial mortgagebacked securities (“CMBS”) include securities that reflect an interest in, and aresecured by, mortgage loans on commercial real property. Many of the risks ofinvesting in CMBS reflect the risks of investing in the real estate securing theunderlying mortgage loans. These risks reflect the effects of local and othereconomic conditions on real estate markets, the ability of tenants to make loanpayments, and the ability of a property to attract and retain tenants. CMBS maybe less liquid and exhibit greater price volatility than other types of mortgage- orasset-backed securities. Convertible Securities Risk: Convertible securities are subject to the risksaffecting both equity and fixed income securities, including market, credit,liquidity, and interest rate risk. Convertible securities tend to be more volatilethan other fixed income securities, and the markets for convertible securitiesmay be less liquid than markets for common stocks or bonds. To the extent thatthe Fund invests in convertible securities and the investment value of theconvertible security is greater than its conversion value, its price will likelyincrease when interest rates fall and decrease when interest rates rise. If theconversion value exceeds the investment value, the price of the convertiblesecurity will tend to fluctuate directly with the price of the underlying equitysecurity. A significant portion of convertible securities have below investmentgrade credit ratings and are subject to increased credit and liquidity risks. Inflation-Linked Investments Risk: Unlike traditional fixed income securities,the principal and interest payments of inflation-linked investments are adjustedperiodically based on the inflation rate. The value of the