The development of new drugs that can be valuable for the evolution of diseases' treatment is a goal for different areas of research, namely natural products chemistry, molecular biology and biochemistry, pharmacology, medicinal chemistry, synthetic organic chemistry and analytical chemistry. Nature is the main source of compounds for pharmaceutical purposes, either by providing the natural organic chemical compounds of interest or as a source of inspiration for the design of new drugs. The known anti-inflammatory and anticancer agents belong to a great diversity of structural skeletons since inflammatory and cancer processes involve many different biological targets. Their origins extend to plants, fungi, bacteria, and marine organisms, besides those produced by semi-synthesis and total synthesis. The tasks of the organic chemist are the screening, the structure assignment, and the semi and total syntheses of active molecules. Herein the screening and assignment of new active structures is addressed, together with other aspects, namely the improvements, both in availability and in effectiveness of action that can be achieved from new derivatives by synthetic or semi-synthetic strategies. Some aspects of drug delivery of anti-inflammatory and anticancer agents are considered. The bibliography presented is far from being exhaustive due to the prodigious number of published works. Instead, the most significant contributions in the scope of this review are described. The active compounds are organised by their biosynthetic origins as terpenoids; macrolides, polyketides and ansamycins; phenolics; alkaloids; peptides; glycoconjugates; other compounds, and food compounds.