Surface modified and bioconjugated quantum dots (QDs) are of central importance in biomedical applications. In this regard, particularly I-III-VI QDs are of specific interest for biosensors, multimodal imaging, chemotherapy and for phototherapy in theranostic applications. Surface modification allows management of the physico-chemical properties, biocompatibility, and pharmacological properties. This review is anticipated to provide an introduction to new researchers about I-III-VI type QDs relating to their synthesis, optical properties, surface modification, bioconjugation, and their applications in biosensors, biological imaging, drug delivery, photothermal therapy and photodynamic therapy. We also highlight introducing magnetic metals and nanoparticles to these QDs for multimodal imaging applications and have addressed toxicity related issues. Finally, we summarize the results obtained and give a short outlook on future directions of I-III-VI based QDs for biomedical applications.