Cactaceae is a botanical family composed of arborescent, shrub, climbing, globose, discoid or epiphytic species, being almost all endemic to the Americas. Cactaceae occurs between latitudes 35º North and South, both at sea level and up to over 5000m altitude. In this way, their species have the capacity to grow in different ecosystems. However, the greatest diversity is found in arid and semi-arid regions, where they are important sources of resources for several species of vertebrates and invertebrates, mainly in the drought season, when there is a great shortage of resources. In addition, some species of cacti represent an important source of food resources for humans and their herds, as well as having enormous ornamental value. Thus, cacti have always aroused the because of their morphological peculiarities and chemical properties. Due to this, cacti have now been the subject of diverse studies. This book brings studies of several areas of plant biology, ecology, conservation and uses of cacti. The first four chapters compose the part related to ecology and conservation. Several species of Cactaceae in Brazil and the world are seriously endangered, with about 31% of the family categorized as threatened. Chapter 1 discusses the importance and how the ex situ conservation of cacti is carried out in the Botanical Garden of Rio de Janeiro in Brazil. In Chapter 2, the authors carried out population studies of two species of endemic cacti of Chapada Diamantina, Brazil, in order to evaluate the population structure of the species for decision-making in relation to their conservation. In Chapter 3, authors studied the biogeography and conservation of Discocactus species that are endemic to South America. In Chapter 4, the authors discuss the floral morphology and the ecological interactions highlighting the importance of conservation of cacti for ecosystems maintenance. Chapters 5 to 10 address issues related to the uses and significance of cacti. Chapter 5 discusses cacti of the genus Pereskia with a healthy diet alternative due to its nutritional properties. The toxicological evaluation, antinociceptive and anti-inflammatory effects of plant extracts is discussed in Chapter 6, specifically, roots of Cereus jamacaru. In Chapter 7 the use of fibers from Opuntia species in the manufacture of Agave juice is evaluated, due to the importance of including fibers in human consume, because dietary fiber may contribute in the prevention of chronic diseases such as diabetes, cancer and cardiovascular illnesses. The antioxidant activity of prickly pear of Opuntia is discussed in Chapter 8, because besides betalains, prickly pear contains vitamins and phenolics. In Chapter 9, the research describes the industrial applications of the berry as well as key points for future research. And in Chapter 10, bioactive compounds of Opuntia oligacantha were determined, as well as their antioxidant capacity, antimicrobial activity and shelf life. All the studies presented in this book are of great importance and serve as a basis for further research to be carried out to make the species of the Cactaceae family be seen beyond their ornamental value.