This article introduces the Time Model subprofile of MARTE, a new OMG UML Profile dedicated to Modeling and Analysis of Real-Time and Embedded systems. After a brief presentation of former time modeling elements present in SPT and UML2, we introduce the Time meta-model of MARTE. It defines physical and logical time, timed model elements and their associated properties. We present both the time domain view and the UML representation of the most important concepts. Various time bases (called clocks in the profile) can be correlated using clock relations and constraints, built from a core set predefined in the profile. Constraints are usually collected from scheduling and partitioning decisions taken in the course of design flow for embedded systems. We illustrate this on two simple examples.