The Finnish basic income experimentwas anambitious effort to study basic income in a Nordic welfare state. This paper describes the planning, implementation, and scientific evaluation of the experiment. The randomized treatment group was paid a guaranteed monthly income, which had no impact on disposable income while a person was unemployed but provided a substantial increase in work incentives. We extend previous evaluations by examining the heterogeneity of incentive changes and employment responses across households. Our results reveal improvements in employment only for couples with children, providing an interesting contrast to other in-work credit programs. [ABSTRACT FROM AUTHOR]