The largely unexplored natural world harbours great biodiversity, and provides a unique and rich source of natural products with interesting pharmaceutical activities as well as potential applications for environmental protection. Over the last few years, much attention has been paid to unraveling the structural, compositional and sequential properties of bioactive compounds, but the exploration of new natural resources needs to be developed wisely while keeping sustainability principles in mind. With the help of some developed isolation techniques, researchers have been able to elucidate new extraction methods applicable to both aquatic and terrestrial organisms. Natural products have often been used in medicine, food, fragrances, and pest control. Most likely due to their easy accessibility, terrestrial plants have been the major source of medicinal products, especially for traditional or folk medicine. However, only 10% of over 250,000 plants have been investigated for biological activity. On the other hand, aquatic environments contain over 80% of worlds plant and animal species. In recent years, several bioactive compounds have been extracted from various marine organisms, such as tunicates, sponges, starfish, soft corals, bryozoans, and sea cucumbers, among others. The search for new metabolites from marine organisms has resulted in the isolation of more than 10,000 metabolites, many of which are endowed with pharmacodynamic properties. These natural products are of high commercial value due to their natural source, complete biodegradable properties, lower or no toxicity, and in most cases lower cost compared to synthetic chemicals. Despite the biodiversity in the marine environment overcoming that of the terrestrial environment, the research into the use of natural marine products as pharmaceutical agents and for environmental applications is still in its early stages. In this context, this book highlights some of the most recent advances in natural product discovery over the past few years.