Among factors affecting hydroponic production systems, the nutrient solution is considered to be one of the most important determining factors of crop yield and quality. This chapter aims to explain aspects related to plant nutrition and its effects on production of hydroponic crops, considering basic aspects such as nutrient solutions and their development through the years; components of nutrient solutions (macro and micronutrients), taking into account criteria of nutrimental essentiality in higher plants and their classification, as well as a brief description of their functions in plants; we define the concept of benefic element and its classification, and cite some examples of their addition to nutrient solutions. The concept of pH of the nutrient solution is also defined, as well as its effect on nutrimental availability; osmotic potential of the nutrient solution and its relationship with electric conductivity are discussed, besides their used units and their equivalences, and the influence of both factors on the nutrient uptake in plants; we highlight the importance of oxygenation in the nutrient solution; climate factors affecting nutrient solutions behaviour are also reported, emphasizing on temperature; formulation and preparation of nutrient solutions considering different fertilizer sources and water quality are described as well; finally, we raise topics related to the management of nutrient solutions depending on the species nutrimental needs and on the hydroponic system used, including flow diagrams and figures that facilitate readers comprehension of concepts and principles. Therefore, this chapter aims to be a practical guide to those interested in hydroponic crops, with a strong theoretical support.