Worldwide, vegetables are grown and consumed as the main part of the human diet. A high volume of by-products is generated annually from leaf, stem, root, and tuber vegetables. Phytochemicals are organic compounds formed by plants in their metabolic operations. Phytochemicals enhance the functional traits of food and play a significant role in maintaining ecological balance. Meanwhile, bioactive phytochemicals contribute to economic sectors, such as nutraceuticals, pharmaceuticals, cosmetics, and novel food. This work highlights the nutritional value of by-products from leaf, stem, root, and tuber vegetables. This book discusses the health benefits and applications of phytochemicals derived from processing by-products of leaf, stem, root, and tuber vegetables. Besides, the book highlights the recovery issues and various techniques for developing new applications from these phytochemicals. In addition, the book boosts the circular economy via using phytochemicals from leaf, stem, root, and tuber vegetable bio-wastes for industrial applications (new edible items, pharmaceuticals, and livestock).