This paper examines the use of generational garbage collection techniques for a lazy implementation of a non-strict functional language. Detailed measurements which demonstrate that a generational garbage collector can substantially out-perform non-generational collectors, despite the frequency of write operations in the underlying implementation, are presented. Our measurements are taken from a state-of-the-art compiled implementation for Haskell, running substantial benchmark programs. We make measurements of dynamic properties (such as object lifetimes) which affect generational collectors, study their interaction with a simple generational scheme, make direct performance comparisons with simpler collectors, and quantify the interaction with a paging system. The generational collector is demonstrably superior. At least for our benchmarks, it reduces the net storage management overhead, and it allows larger programs to be run on a given machine before thrashing ensues. 1 Introducti...