Ethiopia is one of the populous countries in Africa next to Nigeria. This is the direct consequence of high fertility rate that is prevailing in the country. Thus the major objective of this study was to determine levels trends and determinants of fertility in Oromia region where the highest TFR was observed for the year 2005. For this purpose data from the 1994 population and housing census of Ethiopia and EDHS(2000 and 2005) were used. To study levels and trends of fertility both direct and indirect procedures of fertility estimation techniques were applied. The result revealed that fertility decline observed for the year 1994 to 2000; however,fertility level remained constant for the year 2000 to 2005. The result of multivariate analysis with an application of Poisson regression for children ever born indicate existence of significant association with some of the socio-demographic variables. To elucidate the finding of the quantitative result further enriched with qualitative data so that most of the why questions have got answer.The book can be used in the study of fertility levels, trends, and determinants in the context of developing countries with reference to Ethiopia.