Platelets are blood components traditionally believed to play fundamental roles in vascular haemostasis and thrombosis. In recent years, platelets have garnered fresh attention for their roles in tumor genesis and progression. On one hand, platelets are found to be actively recruited by various tumors as a vital part of the tumor microenvironment (TME). This has inspired the idea of employing platelets for tumor targeted drug delivery. To this end, various platelet-based devices have been proposed, such as natural platelets, engineered platelets, platelet membrane, or platelet-derived microparticles. On the other hand, platelets are also involved in tumor immunosuppression mechanisms, directing and/or assisting various tumor-associated immune cells. However, in the context of inflammation and autoimmune diseases, platelets can amplify immune responses by promoting immune cell mobilization and activation, thereby exacerbating tissue damage. Thus, there is emerging interest in tumor-associated platelets as a target for therapeutic modulation of the TME and augmentation of anti-tumor immune responses. In this review, we summarize the latest advances regarding the exploitation of platelets for both antitumor drug delivery and immune modulation of the TME.