Technologies used to analyze transcriptomes include: 

• Sanger sequencing of EST (Expressed Sequence Tags) or cDNA library:Sanger sequencing involves sequencing a large number of randomly selected cDNA clones from a cDNA library. ESTs are short sequences (usually a few hundred base pairs) that represent fragments of expressed genes. By sequencing a large number of ESTs, researchers can identify and characterize genes expressed in a particular tissue. 
• DNA microarrays are high-throughput instruments used to measure the expression levels of thousands of genes simultaneously. They consist of thousands of DNA probes immobilized on a solid surface (such as a glass slide), which hybridize to complementary target sequences in a sample. 
• Serial analysis of gene expression (SAGE) involves the generation of short sequence tags (usually 10-14 base pairs) from the 3' end of mRNA transcripts and are sequenced to identify the expressed genes.
• Cap analysis of gene expression (CAGE) captures the 5' end of mRNA transcripts using a specialized cap-trapping method and sequences them to quantify gene expression.