A report's introduction summarises the contents by describing the purpose of the report and giving an overview of the main ideas expressed within it. Although the introduction is the first section of a report, it is the last section the report writer completes. After all, you can't summarise something that doesn't exist or is incomplete.
Consider who your reader will be and the knowledge he will bring to the report. For example, while you may introduce technical terms in the body of the report, your reader may not be aware of their meaning while reading the introduction.
State the problem addressed in the report and explain why the problem is significant. Depending on the complexity of both, this may be done in one or two sentences.
Describe the purpose or goal(s) of the report--what you were asked to accomplish.
Provide general background information the reader needs to know to understand the report, such as the methods and theories used to gather the information.
Explain the scope of the report's contents, including what is covered and, if necessary, what is not covered. For example, your report may include findings made during an investigation but not recommendations about how to respond to those findings.