The plasma membrane H +  -ATPase of fungi and plants is a single polypeptide of fewer than 1,000 residues that extrudes protons from the cell against a large electric and concentration gradient. The minimalist structure of this nanomachine is in stark contrast to that of the large multi-subunit F O  F 1  ATPase of mitochondria, which is also a proton pump, but under physiological conditions runs in the reverse direction to act as an ATP synthase. The plasma membrane H +  -ATPase is a P-type ATPase, defined by having an obligatory phosphorylated reaction cycle intermediate, like cation pumps of animal membranes, and thus, this pump has a completely different mechanism to that of F O  F 1  ATPases, which operates by rotary catalysis. The work that led to these insights in plasma membrane H +  -ATPases of fungi and plants has a long history, which is briefly summarized in this review.