This volume presents an approach to the formal object-oriented specification of information systems. The approach focuses on the early phases of system development where existing systems have to be described or systems to be developed have to be prescribed (requirements specification or conceptional modeling). Systems are considered to be reactive systems composed from objects that evolve concurrently in a discrete, event-driven way. Based on a temporal logic framework, the language TROLL is defined. TROLL supports the integrated specification of structural and behavioural properties of objects, as well as abstractions like roles, specifications and composite objects. Furthermore, concepts for constructing systems specifications from parts are introduced. Finally, the approach is related to similar ones and discussed.