In allergology, skin tests (ST) are one of the main tools. Their simplicity, rapidity of the result, low cost, near absence of risk make them complements of choice to the patient history which remains the crucial step of the diagnosis. ST demonstrate in vivo the capacity of the cutaneous mast cells to potentially react to allergens. Their sensitivity is good, some precautions have to be taken into account (no antihistaminic drugs, quality of the extracts). Specificity is also good, but a positive test (which is suggestive of the presence of IgE) not always predicts clinical allergic manifestations. Knowledge of limits and pitfalls of ST is of major importance, especially when it comes to selecting extracts for specific immunotherapy and to investigate severe anaphylactic reactions to food or drugs.