Transaction processing is an established technique for the concurrent and fault-tolerant access of persistent data. While this technique has been successful in standard database systems, factors such as time-critical applications, emerging technologies, and a re-examination of existing systems suggest that the performance, functionality and applicability of transactions may be substantially enhanced if temporal considerations are taken into account. That is, transactions should not only execute in a "legal" (i.e. logically correct) manner, but they should meet certain constraints with regard to their invocation and completion times. Typically, these logical and temporal constraints are application-dependent. This text addresses some fundamental issues for the management of transactions in the presence of such constraints. It discusses issues regarding timing estimates, the software and hardware architectures, and the target applications; in detail, for some instances. While the research described in this book is based on a specific model, the results may be generalized to others. Therefore, the issues raised, and the techniques developed, represent several fundamental considerations in the management of time-constrained transactions. The work provides a basis for further directions in research in diverse areas such as database technology, distributed systems, real-time systems, fault tolerant systems, and scheduling theory.