Since 2003 there has been an explosion in the observation of new hadronic states that cannot be classified by the well-tested quark model of mesons (quark-antiquark) and baryons (three quarks or antiquarks). The properties of these states indicate that they are combinations of four, five, or more, quarks and antiquarks, making them manifestly exotic. A recent high-profile example was the discovery of two pentaquark candidates by the LHCb collaboration at the CERN Large Hadron Collider (LHC). No scientific consensus has yet emerged to explain the exotic hadron spectrum, demanding a new set of experimental observations that will feed the development of theoretical models to describe the dynamics of multiquark states.

To explain the current situation in this rapidly developing field, Professor Tim Gershon has co-authored an IoP eBook entitled "Tetraquarks and Pentaquarks". Aimed at a pedagogical level, the eBook provides a tour of quantum chromodynamics, explains about the latest research into the physics of exotic hadrons and describes the exciting opportunities that are offered by the next generation of particle physics experiments. It can be freely downloaded from http://iopscience.iop.org/book/978-0-7503-1593-7

• Publication: http://iopscience.iop.org/book/978-0-7503-1593-7
• DOI: 10.1088/978-0-7503-1593-7