Abstract Kinematic dynamo action in an unbounded homogeneous, fluid conductor is studied from an exact, analytical viewpoint, by exploiting the mathematical tractibility of “helical symmetry,” uncovered by Lortz [1968a). The principal motivation is to elucidate how helical dynamos operate, to clarify their energetics, to extend Lortz's work where possible and to place helical dynamos within the more general context of dynamo theory. Lortz's novel helical coordinate system is first motivated and derived rationally. The velocity and magnetic fields are then projected onto helical coordinates and represented in terms of helical defining scalar functions dependent on only two helical coordinates. The unsteady dynamo equations, in helical variables, are next derived, and their invariance properties deduced. Attention is then focused on the steady state. Low order finite Fourier expansions for the dependence on the primary helical coordinate are introduced. Three different possible low order dynamo classes are ...