This document provides an overview of DNA microarrays, also known as DNA chips. It discusses the principles and techniques used to prepare DNA microarrays, including photolithography. There are two main types of DNA chips: cDNA-based chips and oligonucleotide-based chips. DNA microarrays have various applications, including gene expression profiling, drug discovery, and diagnostics. They provide the advantage of analyzing thousands of genes simultaneously but also have disadvantages such as high costs and complex data analysis.