We present spectral line observations towards the Monoceros PDR in Rosette in context with optical (DSS), far-infrared (C+, KAO), and mid-infrared (Spitzer) imaging of the region. The new data include maps in CO isotopomeric lines (IRAM 30 m, APEX, and NANTEN2) and cuts through the interface in a variety of chemical tracers and transitions: HCN, HNC, HCO+, CN, CCH, and CS, in some cases including rarer isotopomers (IRAM 30 m and APEX). Our goal is to study, and possibly resolve, the temperature, chemical, and density structure in the clumpy PDR/molecular cloud transition. As a first results, we do find evidence for a layered structure perpendicular to the impinging UV radiation in selected chemical and excitational tracers.