In this chapter, some of the latest developments in the groups of natural products collectively known as the quinolin/one, quinazolin/one, and acridone alkaloids are presented. Emphasis is placed on their biogenesis, biological activities, and natural distribution. Quinolin/ones and acridones undoubtedly occur in greatest abundance in plants from the Rutaceae family. The 2-alkylquinolin/4(1H)-ones are typical constituents of the Rutaceae but, surprisingly, they have also been isolated from some bacteria, mainly from Pseudomanas. Fungus Penicillium has yielded a novel class of quinolin/ones, which is based on the combination of amino acids l-valine and l-isoleucine, anthranilic acid, and acetic acid, or these amino acids and tryptamine. They constitute two small groups quinolactacins and quinocitrinines, which are alkaloid types at present unknown from any other source. Quinazoline derivatives are less common in Rutaceae, and a variety of them are produced by bacteria, fungi, and marine animals. In recent years, a number of these alkaloids have been found to possess real pharmacological activity, which is discussed. © Springer-Verlag Berlin Heidelberg 2013.