A novel approach to analytical mechanics, using differential-algebraic equations, which, unlike the usual approach via ordinary differential equations, provides a direct connection to numerical methods and avoids the cumbersome graphical methods that are often needed in analysing systems. Using energy as a unifying concept and systems theory as a unifying theme, the book addresses the foundations of such disciplines as mechatronics, concurrent engineering, and systems integration, considering only discrete systems. Readers are expected to be familiar with the fundamentals of engineering mechanics, but no detailed knowledge of analytical mechanics, system dynamics, or variational calculus is required. The treatment is thus accessible to advanced undergraduates, and the interdisciplinary approach should be of interest not only to academic engineers and physicists, but also to practising engineers and applied mathematicians.