This book is about "Genetic Diversity and Genetic Origin of Weedy Rice growing in rice fields In Districts of Kurunegala and Matara in Sri Lanka". Weedy rice (Oryza sativa f. spontanea), one of the most troublesome rice weeds, first reported in the Eastern Province of Sri Lanka in early 1990s and at present spreading into many rice growing areas. Weedy rice (WR) variable in height, panicle form, grain size, awn length, flag leaf, and growth duration and is a serious problem because of high competitiveness with cultivated rice, variable dormancy and shattering nature of grains. The study were to determine the genetic diversity and differentiation of WR populations from Matara and Kurunegala Districts in Sri Lanka and to explore the possible origin of these WR populations by comparing their genetic relationships with rice varieties (O. sativa) and wild rice (O. nivara and O. rufipogon).