The Journal of Economic Literature (JEL) classification codes are one way of representing the range of economics subjects and subareas. There, Industrial Organization, one of 20 primary categories, has 9 secondary categories, each with multiple tertiary categories.[16] The secondary categories are listed below with corresponding available article-preview links of The New Palgrave Dictionary of Economics Online and footnotes to their respective JEL-tertiary categories and associated New-Palgrave links.