1 Introduction.- 2 Background Material on Domain Decomposition.- 2.1 Introduction.- 2.2 Domain Decomposition for 1-d Problems.- 2.3 Domain Decomposition Methods for Elliptic Problems.- 3 Partial Differential Equations on Graphs.- 3.1 Introduction.- 3.2 Partial Differential Operators on Graphs.- 3.3 Elliptic Problems on Graphs.- 3.4 Hyperbolic Problems on Graphs.- 4 Optimal Control of Elliptic Problems.- 4.1 Introduction.- 4.2 Distributed Controls.- 4.3 Boundary Controls.- 5 Control of Partial Differential Equations on Graphs.- 5.1 Introduction.- 5.2 Elliptic Problems.- 5.3 Hyperbolic Problems.- 6 Control of Dissipative Wave Equations.- 6.1 Introduction.- 6.2 Optimal Dissipative Boundary Control.- 6.3 Time Domain Decomposition.- 6.4 Decomposition of the Spatial Domain.- 6.5 Space and Time Domain Decomposition.- 7 Boundary Control of Maxwell's System.- 7.1 Introduction.- 7.2 Optimal Dissipative Boundary Control.- 7.3 Time Domain Decomposition.- 7.4 Decomposition of the Spatial Domain.- 7.5 Time and Space Domain Decomposition.- 8 Control of Conservative Wave Equations.- 8.1 Introduction.- 8.2 Optimal Boundary Control.- 8.3 Time Domain Decomposition.- 8.4 Decomposition of the Spatial Domain.- 8.5 The Exact Reachability Problem.- 9 Domain Decomposition for 2-D Networks.- 9.1 Elliptic Systems on 2-D Networks.- 9.2 Optimal Control on 2-D Networks.- 9.3 Decomposition of the Spatial Domain.