Cardiolipin (CL) is an important component in prokaryotic and in eukaryotic inner mitochondrial membrane. In humans, CL is made by cardiolipin synthase from phosphatidylglycerol and cytidinediphosphatediacylglycerol. Due to its four acyl chains and small head group, CL can organize into domains which can be protonsinks, fill cavities at protein interfaces, stabilize protein oligomers, and participate in high-curvature membrane regions. Autoantibodies to CL have been found in patients with anti-phospholipid syndrome and lupus. Amino-CL can be modified with or attached to amine reactive probes/surfaces.