Forest ecosystems cover around 31% of the total land area of the Earth. They represent important biodiversity and genetic resources; provide material goods, including fuelwood, commercial timber, soils, medicinal plants and others; as well as environmental services, such as cleaning air and water, sequestering carbon and maintaining biodiversity. Old-growth forests are those developed during long periods without relevant human impact and with distinctive features in terms of forest continuity, structural heterogeneity, large volumes of standing and fallen deadwood, decaying ancient and veteran trees, and large diameter live trees. These characteristics ensure the growth and dispersal of forest-dwelling species, playing thus a vital role in the conservation of biodiversity. This book discusses the ecology, habitat and conservation of old-growth forests, as well as coniferous forests.