In June 1970, a diverse group of scientists attended the International Symposium on the Biology of the Sipuncula and Echiura at the Marine Biological Station in Kotor, Yugoslavia. Forty-two years later in June 2012, an aspiring generation of like-minded scientists convened the Second International Symposium on the Biology of the Sipuncula (ISBS2) along the banks of the Fort Pierce Inlet to the Indian River Lagoon in Florida, USA. The primary objective of the second symposium was to collect the world's dedicated sipunculan biologists in one place for a long overdue face-to-face communication of past, present and future research. We met our objective. This proceedings volume includes a brief summary of workshop discussions and field events, and a compilation of selected research papers presented by an international group of sixteen scientists from twelve nations in attendance at the ISBS2. Herein, we highlight molecular, developmental, morphological, ecological and biogeographic diversity of adult and larval sipunculans. And, we introduce several of the outstanding research challenges associated with resolving sipunculan interrelationships, establishing standard sets of taxonomic characters, refining methods for identification of cryptic species, reconstructing an evolutionary framework of developmental life history patterns, and addressing implications of recent phylogenetic and phylogenomic hypotheses that have relocated the ancient radiation of unsegmented sipunculan body plans within the predominantly segmented Annelida.--Provided by publisher.