In this tutorial, we will address the system design and implementation aspects of multiple input, multiple output (MIMO) communications, especially from a tactical network perspective. We will start with the theory of MIMO communications and end with the implementation aspects of MIMO applied to tactical network communications. In the first part of this tutorial, we will give an overview of MIMO communications. We will cover fundamentals of MIMO communications, including propagation and channel models, transmitter/receiver design, diversity-multiplexing gains, and precoding. We will provide highlights of information-theoretic capacity analysis of MIMO and demonstrate gains relative to single antenna systems. We will use the point-to-point MIMO channel discussion as the starting point, and extend it to multiuser MIMO channels. We will describe various canonical networks that constitute a general mobile ad hoc network (MANET), and address the achievable rates for each of the canonical networks accounting for effects of channel estimation, feedback and interference management mechanisms. The first part of the tutorial will provide the audience with the necessary tools to analyze MIMO communication technologies for dynamic multiuser channels. We will discuss various open problems and future directions to improve legacy communications systems with MIMO. In the second part of this tutorial, we will cover applications of MIMO communications to tactical networks. We will discuss the model for a MANET and address challenges on how to tailor MIMO communications to the network environment. We will cover the cross-layer design aspects for MIMO communications and focus on PHY, MAC and network layers. We will describe channel access and routing mechanisms to enable the PHY-layer MIMO gains. We will discuss different notional scenarios for MIMO communications in a tactical network and describe potential simulation, emulation and testbed environments to develop and evaluate MIMO network communications. Finally, we will discuss radio implementation of MIMO, spanning from the description of software-defined radio (SDR) platforms to the implementation of software and hardware communication blocks. The second part of the tutorial will expose the audience with the necessary tools to develop MIMO technologies for network environments. We will present open problems and future directions to enable the application of MIMO in a tactical network.