In this review, we summarise new insights into diagnostic approaches and treatment strategies for coronary artery disease (CAD) in patients with diabetes mellitus (DM). Despite the improvements in therapy, the clinical management of DM patients remains challenging as they develop more extensive CAD at a younger age and consistently have worse clinical outcomes than non-DM patients. Current diagnostic modalities as well as revascularisation treatments mainly focus on ischemic lesions. However, the impact of plaque morphology and composition are emerging as strong predictors of adverse cardiac events even in the absence of identified ischemia. In particular, the presence of vulnerable plaques such as thin-cap fibroatheroma (TCFA) lesions has been identified as a very strong predictor of future adverse events. This emphasises the need for an approach combining both functional and morphological methods in the assessment of lesions. In particular, optical coherence tomography (OCT) has proven to be a valuable asset by truly identifying TCFAs. New treatment strategies should consist of individualised and advanced medical regimens and may evolve towards plaque sealing through percutaneous treatment.