The history, analysis, recovery, and utilization of O-acetylgalactoglucomannans (AcGGM for short), which is the main hemicellulose present in softwoods, is reviewed. The water-soluble and hence easily extractable AcGGM from Norway spruce (Picea abies) is especially in focus. The influence of different extraction and purification methods on the yield and structure of AcGGM is discussed. Mild structure-preserving processing is vital to maintain the acetyl groups. Without acetyl groups, the water-solubility is decreased due to molecular orientation and the formation of inter- and intramolecular hydrogen bonds. Specific enzymes acting on AcGGM can be useful in targeted modifications, as well as in structure elucidation and structure-function studies. Large-scale recovery methods are also compared. Of particular interest is the recovery of dissolved AcGGM from process waters in mechanical pulp mills using Norway spruce as raw material. AcGGM has promising biological activity and physico-chemical properties suitable for various applications in, for example, food, health, papermaking, textile, and cosmetic industries.