In this special session we explore holistic approaches to hardware/software debug that use or integrate transaction level models (TLMs). We present several TLM-based approaches to system-level diagnostics, ranging from use of most popular transaction level modeling languages through to hybrid technologies that combine TLMs with other well known diagnostic tools like in-silicon trace logic. Categories and Subject Descriptors C.5 [COMPUTER SYSTEM IMPLEMENTATION] General Terms Measurement, Design, Standardization, Verification. Keywords Transaction-level models, system diagnostics.