The design and optimization of rateless codes for Slepian-Wolf encoding are considered. Rateless codes are proposed to address two shortcomings of currently available Slepian-Wolf schemes: their fragility to changing source statistics, and their inability to guarantee successful decoding for practical block length. We propose a novel type of optimized rateless code, called a Matrioshka code, to deal with the particular conditions of Slepian-Wolf encoding.