Neuroendocrine tumors (NET) are rare heterogenous tumors which prevalence is increasing. Their features vary by anatomical location, functionality and hormonal production. Their management needs a multidisciplinary approach. Functional tumors develop characteristic clinical syndromes in contrast to non-functional tumors that are diagnosed fortuitously or at advanced stage. NET can secrete many specific and general biomarkers. CgA is the most sensitive general marker. Its value should be interpreted along with the renal function and the gastrin level. Some new biomarkers such as NTproBNP, proGRP and NET gene transcripts have been identified. The latter are not yet routine in clinical practice. We present In this review biological biomarkers involved in NET with a focus on the assays and their use in clinical practice.