In this report, we present the BOBILib, a collection of more than 2500~instances of mixed integer linear bilevel optimization problems. The goal of this library is to make a large and well-curated set of test instances freely available for the research community so that new and existing algorithms in bilevel optimization can be tested and compared in a standardized way. The library is sub-divided into instances of different types and also contains a benchmark instance set. Moreover, we present a new data format for mixed integer linear bilevel problems that is less error-prone compared to an older format that will now be deprecated. We provide numerical results for all instances of the library using available bilevel solvers. Based on these numerical results, we select the benchmark instance set, which provides a meaningful basis for experimental comparisons of solution methods in a moderate time. Each instance, together with a solution file if a feasible point or an optimal solution is known, can be downloaded at https://bobilib.org.