The plant world-plants, algae and fungi-is an extraordinary source of bioactive molecules that can be exploited in the pharmaceutical, food, cosmetics, and skincare industries. This source has been known since the dawn of time. In recent decades, thanks to manufacturing, the by-products of several industries can be used as raw materials for the extraction of value-added molecules. Their use in the food, cosmetics, and pharmaceutical industries has become a major economic and environmental challenge. Extensive research has been undertaken to identify bioactives in plants, algae, and micro-organisms. Among these molecules, particular attention has been paid to their anti-inflammatory and antioxidant activities. Numerous studies have been carried out on by-products or cultivated plants; few investigations have focused on species used in traditional and popular medicine around the world. Measurement methods limit the comparison of information, and assessment of their activities remains confined to minor uses. The evaluation of skin care creams, biological effects, and antimicrobial and anti-tumor effects require further research. The following Special Issue includes publications exploring the anti-inflammatory and antioxidant properties of natural compounds, their distribution in organisms, measurement methods, ways to increase extraction, and their effects on the development of new drugs, foods, and skin care products.