Endogenous Ca2+ activated Cl- channels (CaCC) demonstrate biophysical and pharmacological properties also found in cells overexpressing TMEM16A (anoctamin 1, ANO 1), a protein that has been recently identified as CaCC. Proteins of the anoctamin family (TMEM16A-K, anoctamin 1-10) are expressed abundantly. The number of reports demonstrating their physiological and clinical relevance is quickly rising. TMEM16A null mice exhibit severe defects in epithelial transport along with tracheomalacia and death within one month after birth. TMEM16-proteins have also other interesting properties that may be related to cell swelling, control of cell volume, and apoptosis. Available data suggest that TMEM16-proteins form stable dimers. However, despite its outstanding physiological significance, the mechanisms for activation of TMEM16A are unclear. TMEM16A is activated upon increase in intracellular Ca2+, but we don’t know whether Ca2+ binds directly to the channel or whether additional components are required. We demonstrate that TMEM16A is strictly membrane localized and requires cytoskeletal interactions to be fully activated. Despite the need for cytosolic ATP for full activation, phosphorylation by protein kinases is not required. In contrast, the Ca2+ binding protein calmodulin appears indispensable and interacts physically with TMEM16A. Openers of small and intermediate conductance Ca2+ activated potassium channels like 1-EBIO are known to interact with calmoduline and also activate TMEM16A. Our present results suggest the use of these compounds for activation of electrolyte secretion in diseases such as cystic fibrosis.