Progress in Computing Applications Muhammad Ijaz Ijaz, Mustafa Hameed Ghulam Mustafa 5 2 2016 http://www.dline.info/pca/fulltext/v5n2/pcav5n2_2.pdf In this paper formal methods are discussed for software engineering. Formal methods are very important for critical systems development where system properties such as security, reliability, and safety are very important. Critical systems have very high validation costs and the costs of system failure are large and increasing. Formal methods can reduce these costs. They are used to improve the software quality, reliability, usability, dependability and maintainability. Formal methods based on mathematical models; two basically tools are used to build the mathematical model that are logics and set theory. Formal techniques use the discrete mathematics and mathematical logics. Formal methods also provide the correctness proofs. The formal method’s area of application is requirement analysis, specification, design & implementation and verification & validation that are briefly discussed. In this paper the some important formal methods, techniques and their importance is elaborated with example. Especially propositional logic and Calculate assignment are also discussed with examples.