The Condensable Particulate Matter (CPM) fraction of PM 2.5 must be evaluated in permits and air planning since 2011. EPA Method 202 is now in its fourth iteration, but lack of replicability, even during different runs in the same test continues to be a problem. Precursors, secondary formation and test artifacts add additional complexity. As ambient levels are lowered, the accuracy of mass-based approaches decreases significantly as you approach the (unknown for Method 202) detection level. Kevin Crosby will review the evolution of condensable particulate test methods and guidance as they address known issues. Zach Emerson will summarize the state of current research on CPM Methods and the precursor bias associated with NH3, SO2 and moisture and will discuss bias adjustment approaches. Rich Trzupek will outline the impact of lower-level measurements in interpreting test results and present new research on precursor bias, followed by a speaker panel and Q & A session. Permittees and permit writers need to understand the strengths and weaknesses of CPM test methods.