Even Though Thin Solid Films Have Found Tremendous Applications In Electronic, Optical And Other Industries The Basic Concepts About Them Have Often Been Taken Similar To Those Of The Bulk Materials From Which Films Are Prepared And These Need Not Be So. This Book Is Intended To Serve As A Guide To Students, Beginners And Research Workers Interested In This Field.The Basic Science Behind Thin Solid Films Has Been Described With Special Reference To Nucleation, Structures Of Films, Their Growth Process, Phase Transitions, Behaviour Of Films Under Electrical, Electromagnetic And Other Fields With Film Thickness, Temperatures Etc. Characteristic Behaviour Of Films, Different From Bulk, Can Often Be Related To Nearly Two-Dimensional Nature Of Films And Also To The Presence Of Factors Such As Surface States, Contact Potential, High Defect Concentration, Creation Of New Energy Levels, In-Homogeneities, Discontinuities Or Gaps, Etc. Which Are More Often Less Significant In Bulk Materials. Special Techniques Used For Measuring Thin Film Properties And Also Precautions To Be Taken Have Been Given In Details. This Book Also Includes Many Useful Relations Otherwise Scattered In Literatures And Also A Good Number Of References Though Not Complete But Relevant To The Topics Discussed.