As　XML　has　become　a　standard　format　for　data　exchange　and　data　representation,　ensuring　the　correctness　of　concurrent　update　on　XML　data　becomes　a　critical　issue.　This　paper　presents　an　overview　of　some　of　the　most　important　XML　concurrency　control　protocols　so　far,　such　as　locking-based,　timestamp-based　and　optimistic　XML　concurrency　control　protocols.　Summary　and　comparison　are　given　for　each　protocol　from　point　of　implementation　principle,　optimistic　algorithm,　multiversion　technology　and　serializability　aspects.　Some　current　researching　trends　in　XML　concurrency　control　protocols　are　discussed.　©　2012　Springer-Verlag.