Biochips are collections of miniaturized test sites (microarrays) arranged on a solid substrate onto which a large number of biomolecules are attached with high density. Like a computer chip performing millions of mathematical operations in a few split seconds, a biochip allows for simultaneous analyses of thousands of biological reactions, such as decoding genes, in a few seconds. Biochip technologies can be applied to numerous fields including genomic, proteomic, and glycomic research, as well as pharmacology and toxicology. However, one of the most common applications is in the determination of gene expression in human cells and tissues. Global gene expression analysis has helped to identify important genes and signalling pathways in human malignant tumors. And there is hope that microarrays will make the step from "the (laboratory) bench to the bedside (of the patient)". Recent studies have indeed revealed that analysis of differential gene expression by microarrays may help to identify subtypes of malignant tumors, that allow a risk stratification of the patients. However, there are several issues that need to be addressed before microarrays may become a tool for routine diagnostics, such as problems with bioinformatic analysis, construction of disease or tissue specific microarrays with only limited numbers of genes of interest, standard operation procedures for tissue preparation to prevent RNA degradation, etc.. In this article, an overview over of the multifarious biochip applications and technologies, its limitations, challenges and future developments is provided.