Reionization is a complex process whereby hydrogen (and helium) in the Universe is ionized by the radiation from first luminous sources. Theoretically, the importance of the reionization lies in its close coupling with the formation of first cosmic structures and hence there is considerable effort in modelling the process. In this talk, I will present our recent works on some aspects of this subject. In particular, I will give an overview of the semi-analytical approach (Choudhury & Ferrara (2005,2006)) to study the observational constraints on reionization. We implement and investigate a method to do a detailed statistical analysis using Principal Component Analysis (PCA) technique. We also discuss different observations related to reionization and show how to use PCA for constraining the reionization history.