It is our great pleasure to present the proceedings of the Third International Workshop on Multiple Access Communications (MACOM) that was held in Barcelona during September 13–14, 2010. In 1961, Claude Shannon established the foundation for the discipline now known as “multi-user information theory” in his pioneering paper “Two-way Communication Channels,” and later Norman Abramson published his paper “The Aloha System—Another Alternative for Computer Communications” in 1970 which introduced the concept of multiple access using a shared common channel. Thereafter, for more than 40 years of study, numerous elegant theories and algorithms have been developed for multiple-access communications. During the 1980s and 1990s the evolution of multiple-access techniques p- ceeded in conjunction with the evolution of wireless networks. Novel multiple access techniques like code division multiple access (CDMA) and orthogonal frequency division multiple access (OFDMA) provided increased spectral - ?ciency, dynamicity and ?exibility in radio resource allocation with intrinsic anti-multipath and anti-interference features. In this ?rst decade of the 21st century,multiple-accesstechniques,derivedfromadvancedwirelesstransmission methodologiesbasedonthediversityconcept(e. g. ,MC-CDMA,MIMO-OFDMA and SC-FDMA), opened the road to a renewed idea of multiple access. Today multiple-access communications involve many challenging aspects not only l- ited (like in the past) to physical layer design. Medium access control (MAC) techniques play a crucial role in managing the radio resources that users will exploit to transmit their data streams. Recent developments in software radios and cognitive radios have led to a signi?cant impact also on spectrum m- agement and access paradigms.