This is a graduate-level introduction to formal methods. The first part presents two formal languages: logic, in various forms, and Communicating Sequential Process (CSP) as a process algebra. The second part offers specification and testing methods for formal development of software. Building on the foundations from the first part, the reader is allowed to embrace methods for practical applications. The reader will find the examples cutting across chapters valuable for this purpose. The final section takes the reader further into application domains.