Anti‐platelet factor 4 immunothrombotic syndromes comprise a group of disorders that include heparin‐induced thrombocytopenia and vaccine‐induced immune thrombocytopenia and thrombosis. These are highly prothrombotic, immunological disorders characterised by specific clinical and pathological criteria which include thrombocytopenia and thrombosis. While they are predominantly triggered by heparin and the adenoviral vector vaccines, respectively, other provoking factors have been described, as well as spontaneous forms. The unexplained co‐occurrence of thrombocytopenia with thrombosis should raise suspicion and prompt testing. This nutshell review discusses the pathophysiology, presenting features and diagnostic criteria for these conditions.