Computer networks are an indispensable part of every research organization. Local networks tie together machines within a lab or over an entire campus, allowing users with common goals and interests to share resources such as disks, printers, or supercomputers. Wide area networks operated by the NSF, the Department of Energy, and other funding agencies are mainly used to exchange information but are also increasingly used to access remote resources.
This chapter is an introduction to computer networking for computational scientists. The emphasis is on how scientists are likely to use local and wide area networks. We will describe the types of resources that are available over networks and how to use common networking tools to take advantage of the resources. The emphasis will be on the user's view of networking, with only enough of a description of the hardware and software to give readers a sense of why networks evolved the way they have and where they are headed in the near future.
There are several good books on computer networks for those readers who want to learn more. Two textbooks on network concepts and local area network implementation are by Comer  and Perlman . An informal, easy-to-read description of the Internet (the loosely organized collection of wide area networks that will be described in Section 3) is The Whole Internet Catalog, by Krol . This book is highly recommended for anyone who will be more than a casual user of network resources.