Sigma Guitars is a guitar manufacturing brand originally released by C.F. Martin as a line of guitars at affordable prices to compete with the increasing number of imported guitars from Japan and elsewhere. The Sigma line was discontinued by Martin in 2007. The rights to the name was acquired by German company AMI Musical Instruments GmbH, which relaunched the brand with guitars being produced in China. The current range of Sigma instruments include acoustic and classical guitars, acoustic basses and ukuleles.