Jurassic hardgrounds reflect the complex interplay of sedimentological, diagenetic, and biological processes. Prerequisite for their formation were prolonged periods of omission which favoured synsedimentary lithification near the depositional interface. The fauna associated with hardgrounds reflects the gradual hardening of the substrate passing from a softground through a firmground stage. Most Jurassic hardgrounds formed on carbonate platforms, particularly on high energy submarine shoals where their faunal diversity reaches its peak. Pelagic hardgrounds differ from shallow shelf hardgrounds in displaying thick mineral crusts, low faunal diversity and density, and by the lack of scouring. The high degree of variation in faunal distribution and diversity of hardgrounds demonstrates the difficulties which have to be overcome when studies of community evolution are attempted.