  The Mock LISA Data Challenges are a programme to demonstrate and encourage
the development of LISA data-analysis capabilities, tools and techniques. At
the time of this workshop, three rounds of challenges had been completed, and
the next was about to start. In this article we provide a critical analysis of
entries to the latest completed round, Challenge 1B. The entries confirm the
consolidation of a range of data-analysis techniques for Galactic and
massive--black-hole binaries, and they include the first convincing examples of
detection and parameter estimation of extreme--mass-ratio inspiral sources. In
this article we also introduce the next round, Challenge 3. Its data sets
feature more realistic waveform models (e.g., Galactic binaries may now chirp,
and massive--black-hole binaries may precess due to spin interactions), as well
as new source classes (bursts from cosmic strings, isotropic stochastic
backgrounds) and more complicated nonsymmetric instrument noise.
