Multiple Myeloma (MM) and other plasma cell malignancies initially present as an asymptomatic precursor state, known as monoclonal gammopathy of undetermined significance (MGUS). When confronted to a monoclonal protein in blood or urine tests, physicians should first exclude the presence of a treatment-requiring MM. They should be aware that there are two benign precursor states, that do not require anti-myeloma treatment. Both MGUS and Smoldering Multiple Myeloma (SMM) need an initial visit by a haematologist, with further follow-up tailored to the individual patient and disease characteristics. In the current article we describe both entities, discuss their monitoring and resume the latest publications in their field.