Introduction: Biologic therapy has revolutionized the treatment of immune mediated inflammatory diseases (IMID), such as inflammatory bowel disease (IBD), rheumatoid and psoriatic arthritis, ankylosing spondylitis and psoriasis. Nevertheless, some patients exhibit primary nonresponse (PNR) or secondary loss of response (SLR) to biologics. Areas covered: This collaborative review provides data on the role of therapeutic drug monitoring (TDM) in IMID for optimizing biologic therapy including infliximab, adalimumab, certolizumab pegol etanercept and golimumab vedolizumab, secukinumab and ustekinumab. Expert opinion: Most exposure-response relationship studies show a positive correlation between biologic drug concentrations and favorable therapeutic outcomes in IMID with higher drug concentrations typically associated with more objective outcomes. Clinically, reactive TDM rationalizes the management of PNR and SLR to anti-tumor necrosis factor therapy and is emerging as the new standard of care in IBD as it is also more cost-effective than empiric dose escalation. Preliminary data suggest that proactive TDM with the goal to achieve a threshold drug concentration is associated with better therapeutic outcomes when compared to empiric drug optimization and/or reactive TDM of infliximab and adalimumab in IBD. However, more data from well-designed prospective studies are needed to prove the benefit of TDM-based algorithms in real life clinical practice in IMID.