Barnacles are the most successful group of fouling organisms in the marine environment because of their morphology, life history and population ecology. Like many benthic marine organisms, barnacles have a complex life cycle. In general, the larval phase includes six planktotrophic naupliar stages followed by one non-feeding cypris larval stage. The lecithotrophic cyprids are specialized for locating suitable attachment sites and commencing metamorphosis (both processes are often referred to as "settlement") to juvenile barnacles. It is believed that pelagic cyprids have active behavioral responses to the physical, chemical and biological properties of a substratum surface, which lead to their gregarious settlement. Furthermore, endogenous factors, such as the physiological condition of the cyprids, determine how their attachment and metamorphosis is affected by exogenous stimuli. Thus, this article reviews recent discoveries on the physiological and molecular mechanisms of attachment and metamorphosis in barnacle cyprids. A wide variety of chemical and biological exogenous factors (adult conspecific extract, waterborne pheromones, footprints, neurotransmitters, hormones and biofilms) affect the attachment and metamorphosis of barnacle cyprids. For example, adult conspecific extract is a water-soluble glycoprotein that induces conspecific cypris settlement in its substratum-bound conformation. This adult conspecific extract, which was previously known as arthropodin, is now known as the settlement-inducing protein complex (SIPC). This complex has been isolated from the adult extract, biochemically characterized, genetically cloned, and its expression pattern has been examined during barnacle larval development, attachment and metamorphosis. Similarly, waterborne pheromone is released into the water column by adults and can be detected by cyprids in solution. The waterborne pheromone is a small peptide with a basic carboxy terminus and a neutral, or basic amino terminus, which induces cypris settlement. Cyprids also secrete an antennular footprint, which acts as a secondary cue in larval-larval interactions during settlement. The material basis of footprints for inducing settlement either contains, or is equivalent to SIPC. Neurotransmitters (e.g. acetylcholine, dopamine, serotonin, catecholamines, and noradrenaline) stimulate the secretion of adhesive granules from the cement glands, and the attachment and (or) metamorphosis of cyprids. Likewise, hormones (e.g. methyl farnesoate, juvenile hormone III, 20-hydroxyecdysone and ecdysone mimic RH5849) are reported to induce attachment and (or) metamorphosis of cyprids. Finally, biofilms, which are assemblages of microorganisms and organic molecules, play a key role in the cypris settlement process. Biofilms can facilitate, inhibit or have no effect on attachment and metamorphosis of cyprids, with their role determined by density, composition, physiological condition, and growth phase of the bacteria. The physiological condition of cyprids is mainly controlled by their energy reserves and age, with their energy reserves a major determinant of their physiological quality. A cyprids energy status is measured as an index of their lipid, nucleic acid and protein content. Additionally, the age and ageing temperature of cyprids significantly affects their settlement ability. For example, newly molted cyprids would not yet have gained their settlement ability, but cyprids progressively lose their settlement ability with age. This review provides new insights into the attachment and metamorphosis mechanisms of barnacle cyprids, providing a foundation for developing new, efficient, and less environmentally damaging antifoulants.