Memory profiling in R Thomas Lumley University of Washington R is well-known to be slow and able to handle only small data sets. A critical part of improving the performance of R is the ability to measure performance accurately, and the R profiler has been valuable in improving start-up time and S4 method handling. This success motivates extending the profiler to measure memory use as well as time. I will explain why memory-use profiling is less straightforward than time profiling and describe three memory profiling facilities that have been added to R 2.4.0.