Antibody-Drug conjugates (ADCs) are an emerging class of biotherapeutics that hold enormous promise for effective targeted therapy in oncology and beyond. They combine the strengths of antibodies and small molecule drugs - high specificity and high potency - in a single format. ADCs consist of three elements: antibody, payload drug, and linker. The conjugation of payload and antibody via a linker is a critical aspect that defines ADC quality, safety and efficacy. The linker is designed to be stable in circulation but facilitate effective release of the payload at the site of action. Still, its attachment to the antibody may affect the specificity and stability of the ADC compared to the antibody. Mass spectrometry (MS) is a powerful tool for the characterization of molecular details of large biomolecules. It is particularly useful for monitoring the attachment of linker/payload to an antibody and for assessing the stability of an ADC.