This chapter reviews the discovery of mixotrophy in mycorrhizal plants, the available data on mixotrophic physiology, and the evolutionary link between mixotrophy and full mycoheterotrophy. In usual mycorrhizal associations, the fungus exploits plant photosynthetic carbon (C) and provides mineral resources as a reward, such as nitrogen (N), phosphorous or water collected in the soil by its mycelium. A variant of mycoheterotrophy occurs in plants that initiate their development as mycoheterotrophic seedlings before turning green at adulthood. This initial mycoheterotrophy is known in several basal plant lineages disseminated by spores, but also in plants that form minute seeds with extremely limited reserves and require fungal C to germinate as mycoheterotrophs, such as orchids. Initial mycoheterotrophy may still fit into a mutualistic framework, since the fungus is rewarded in C when plants are adult. Mixo- and mycoheterotrophic plants offer a fascinating, newly and fully open research area, demonstrating the power of mycorrhizal networks in shaping mycorrhizal networks.