We present cKanren, a framework for constraint logic programming (CLP) in Scheme. cKanren allows programmers to easily define, combine, and use different kinds of constraints. cKanren includes constraints over finite domains and disequality constraints over tree terms. cKanren subsumes miniKanren, a logic programming language embedded in Scheme. The cKanren framework is designed to encourage an especially pure style of logic programming in which goals can be reordered arbitrarily without affecting a program’s semantics (with an important decidability-related caveat). We develop the complete implementation of the cKanren framework, written in R6RS Scheme extended with SRFI-39 parameters. We provide the implementation of cKanren’s finite domain and disequality constraint solvers. In addition to these implementations, we provide introductions to miniKanren and cKanren, and numerous example programs, including the Send More Money cryptarithmetic puzzle and Eight Queens.