1 Introduction. - 2 Process Calculus. - 2. 1 Transition Systems. - 2. 2 Hennessy-Mi lner Logic. - 2. 3 Basic Language. - 2. 4 Transitional Semantics. - 2. 5 Strong Bisimulations. - 2. 6 Bisimulations. - 3 Bisimulation and Trace Limits of Agents 37. - 3. 1 Strong Bisimulat ion Limits. - 3. 2 *-Strong Bisi mulation Limits. - 3. 3 Bisimulati on Limits. - 3. 4 Trace Limits. - 4 Limit Behavior of Agents. - 4. 1 Modifications of Topologies on Actions. - 4. 2 Topologies on Agents. - 4. 3 Several Limit Theorems. - 5 Near Bisimulations Defined by Closures. - 5. 1 Near Bisimulations in Transition Systems. - 5. 2 Near Strong Bisimulations. - 5. 3 Near (Weak) Bisimulations. - 6 Bisimulation Indexes Induced by Metrics on Actions. - 6. 1 Bisimulation Indexes in Transition Systems. - 6. 2 Hennessy-Milner Logical Characterization of Bisimulation Indexes. - 6. 3 Strong Bisimulation Indexes. - 6. 4 (Weak) Bisimulation Indexes. - 6. 5 Approximate Communication. - 6. 6 Some Applications: Two Examples in Timed CCS. - 6. 7 Some Appli cations: An Example in Real Time ACP. - 7 Conclusion. - References. Language: English