This chapter deals with underlying principles of chromatography and its mathematical treatment in a lucid manner exemplified with numerical. The chapter discusses about peak resolution, column efficiency, factors affecting retention time, column chemistry, void volume, dead volume, etc. Analogies have been given to explain the concepts of chromatography, which otherwise seems to be cluttered and confusing one. How molecule of interest interact with column phase and how it leads to Gaussian distribution curve in both gas and liquid chromatography has been elucidated in a simplistic manner. Partition coefficients, R-factor, and van Deemter equations have been dealt with practical data to acquaint the students conceptual framework in a pragmatic fashion. Reverse phase and normal chromatography, factors affecting elution of molecule of interest, chromatographic conditions like flow rate, column temperature, mobile phase, column length, column internal diameter, column packing, and particle size have been comprehensively discussed.