Review of the experimental evidence on pentaquarks and critical discussion

We review and discuss the experimental evidence on predicted baryonic states made by 4 quarks and one antiquark, called pentaquarks. Theoretical and experimental advances in the last few years led to the observation of pentaquark candidates by some experiments, however with relatively low individual significance. Other experiments did not observed those candidates. Furthermore, the masses of the $\theta^+$(1540) candidates exhibit a large variation in different measurements. We discuss to which extend these contradicting informations may lead to a consistent picture.