BCL10 (for B cell lymphoma 10), together with CARMA1 (CARD11) and lymphoid tissue lymphoma-translocation gene 1 (MALT1) are signaling proteins. BCL10 was first identified as a gene truncated or mutated in MALT B cell lymphomas and other tumor types. These proteins have a key role in antigen-receptor-mediated lymphocyte activation through the NF-κB pathway. Activation of NF-κB is essential for the immune system to function normally. Deregulated NF-κB in lymphocytes can lead to immunodeficiency, but also to autoimmunity or lymphomas. Phosphorylation of the CARMA1 and BCL10 proteins and ubiquitylation of BCL10 affect the formation and stability of the CARMA1-BCL10-MALT1 (CBM) complex, and also control negative feedback regulation of the NF-κB signaling pathway. Also, recent studies point out an unexpected role for BCL10 in the regulation of the actin cytoskeleton.