CircRNAs are a subclass of lncRNAs that have been found to be abundantly present 
in a wide range of species, including humans. CircRNAs are generally produced by 
a noncanonical splicing event called backsplicing that is dependent on the 
canonical splicing machinery, giving rise to circRNAs classified into three main 
categories: exonic circRNA, circular intronic RNA, and exon-intron circular RNA. 
Notably, circRNAs possess functional importance and display their functions 
through different mechanisms of action including sponging miRNAs, or even being 
translated into functional proteins. In addition, circRNAs also have great 
potential as biomarkers, particularly in cancer, thanks to their high stability, 
tissue type and developmental stage specificity, and their presence in 
biological fluids, which make them promising candidates as noninvasive 
biomarkers. In this chapter, we describe the most commonly used techniques for 
the study of circRNAs as cancer biomarkers, including high-throughput techniques 
such as RNA-Seq and microarrays, and other methods to analyze the presence of 
specific circRNAs in patient samples.