Cotton leaf curl disease (CLCuD) is a major limitation to cotton production on the Indian subcontinent. A survey for viruses causing CLCuD was conducted during the 2009 and 2010 cropping seasons in the northwestern Indian cotton-growing belt in the states of Punjab, Haryana and Rajasthan. Partial sequences of 258 and full-length sequences of 22 virus genomes were determined. This study shows that the resistance-breaking cotton leaf curl Burewala virus (CLCuBuV) is now the dominant virus in many fields. The spread and establishment of the mutant CLCuBuV in northwestern India, the variation in its genomic sequence, its virulence and infectivity, and the implications for cotton breeding are discussed.