Papaver is one of the genera included in the Papaveraceae plant family. All the species of this family have notable alkaloid content, and Papaver alkaloids that were isolated from the species of the reviewed region will be presented and discussed. These plants were used by humans since the dawn of humanity, and traditional uses are well documented. The greater part of this review article will be dedicated to Papaver somniferum because it is the most studied and most published among all Papaver species, including those that are not native to the reviewed region (RR). The chemical compositions of the plants will be extensively presented and discussed, including the factors that affect these compositions. Most of the information will be presented in tables, which enable readers to find it easily. Special attention will be drawn to dangers and toxicity of these plants. Finally, carefully selected, previously published review articles about the Papaver species will also be presented.