Biomarkers, radiology fi ndings, and endoscopic studies, together with clinical assessment of patients with infl ammatory bowel disease, can be used to help determine prognosis, assess disease activity, and increasingly to inform treatment decision-making. This article reviews the current "state of the science" regarding the multitude of different tests that can be performed and how these can be used in the clinic to guide management. Initially, when patients present with symptoms suggestive of infl ammatory bowel disease (IBD), standard endoscopic studies and radiographic studies should be performed and the use of combinations of serologic and fecal markers may additionally be incorporated into patient assessment. Once the patient has a formal diagnosis, prognosis should be assessed and serologic evaluation may be used, but in conjunction with endoscopic and radiographic studies. Within the context of evaluating clinical predictors of disease (e.g., disease location, nutritional status, routine blood tests), early mucosal healing has been linked to better outcomes, and failure to heal the mucosa has been associated with poorer outcomes. Evaluation of response to therapy can be approximated with the use of biomarkers (e.g., C-reactive protein, fecal calprotectin, lactoferrin), and therapeutic drug monitoring has enabled us to assess levels of drug metabolites, drug levels, and antidrug antibodies to guide the ongoing management. Although there is not yet universal adoption of biomarkers to determine treatment choices (e.g., the use of anti-tumor necrosis factor therapy), biomarkers have enabled us to "fi ne tune" treatment of some patients with IBD. Establishing mechanisms of communicating these risks/benefi ts to patients will be a considerable challenge and remains a priority area of research.