The LISA International Science Team Working Group on Data An lysis (LISTWG1B) is sponsoring several rounds of mock data challenges, with t he purpose of fostering development of LISA data-analysis capabilities, and of demonstrating t echnical readiness for the maximum science exploitation of the LISA data. The first round of chal lenge data sets were released at this Symposium. We describe the models and conventions (for LISA and for gravitational-wave sources) used to prepare the data sets, the file format used to encode th em, and the tools and resources available to support challenge participants. The objectives, structure, and timeline of the Mock LISA Dat a Challenges (MLDCs) are discussed in the other contribution in this volume by the MLDC Task Force. Here we concentrate on the technical side of the challenges, and i n particular on the theoretical models used to embody LISA and gravitational-wave ( GW) sources in the first Challenge, and on the file format used to distribute the Chall enge datasets. More details can be found on the official MLDC website [1], in the living Omnibusdocument for Challenge 1 [2], and on the MLDC Task Force wiki [3].