Themes are groups of Mega Bloks sets that are centered around a common subject and often share a common design or storyline. This is the primary method to sort Mega Bloks sets. Over the long history of Mega Bloks, dozens of themes have been introduced or phased out. While earlier themes had a lifetime that spanned several decades and involved the introduction of related subthemes, newer themes are only in production for one or three years in the present, the exception being Bionicle, which lasted for ten years.