We study the existence of strange nonchaotic attractors ͑SNA͒ in the family of Harper maps. We prove that for a set of parameters of positive measure, the map possesses a SNA. However, the set is nowhere dense. By changing the parameter arbitrarily small amounts, the attractor is a smooth curve and not a SNA. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2259821͔In the last two decades there has been an enormous interest in the so-called strange nonchaotic attractors (SNA). These attracting invariant objects of dynamical systems capture the evolution of a large subset of the phase space and are very relevant for their description. In particular, SNA are geometrically complicated (they are strange) and their dynamics is regular (in most of the examples, quasiperiodic). SNA are typically observed in systems where there is a coupling between different dynamics. In contrast to the vast amount of numerical and experimental work in the area, there are only few rigorous proofs. The goal of this paper is to prove the existence and abundance of SNA in the family of Harper maps. This family arises from a model in mathematical physics and it is a paradigm of a 1D quasiperiodically forced map. Our approach connects the spectral theory of Schrödinger operators and the theory of nonuniformly hyperbolic systems. So, even if the proof is made for a concrete family, many of the arguments apply to other families.