In a randomized evaluation, also called a randomized controlled trial (RCT), a random selection of individuals from a sample pool is offered a program or service, while the remainder of the pool does not receive an offer to participate in the program or service. Random assignment ensures that, with a large enough sample size, the two groups (treatment and control) are similar on average before the start of the program. Any difference that subsequently arises between the groups can be attributed to the intervention rather than to other factors. Many real-world challenges may arise during the planning and implementation of randomized evaluations. Several of these challenges can be addressed by designing a randomized evaluation that accommodates existing programs.