Multiple classes of agent with distinct mechanisms of action are now available for the treatment of patients with relapsed and/or refractory multiple myeloma (RRMM), including immunomodulatory agents, proteasome inhibitors, histone deacetylase inhibitors and monoclonal antibodies. Additionally, several different drugs may be available within each agent class, each with their own specific efficacy and safety profile. This expansion of the treatment landscape has dramatically improved outcomes for patients. However, as the treatment options for RRMM become more complex, choosing the class of agent or combination of agents to use in the relapsed setting becomes increasingly challenging. Furthermore, treatment options for specific patient populations such as the elderly, those with high-risk cytogenetic abnormalities and those with refractory disease are yet to be defined in the current treatment landscape. When choosing an appropriate treatment approach, physicians must consider multiple criteria including both patient-related and disease-related factors. The aim should be to provide patient-specific treatment in order to gain a clinical benefit while minimizing toxicity. This review provides an overview of the mechanism of action and efficacy and safety profiles of each class of agent and of treatment regimens that combine different classes of agent, with a special focus on treating specific patient populations.