Most programming languages allow the use of free variables in procedures. The mechanism for connecting such free variables with their intended meanings has significant impact on the convenience of the language for the programmer and the efficiency of the resulting programs. The EL1 programming language in the ECL programming system provides a closure mechanism which allows the programmer considerable control over the binding of free variables and serves as an aid to efficient implementation. In this paper, the closure mechanism for EL1 is explained, its rationale presented, and various applications displayed.