Isaac Slater (1803 – 3 December 1883) was a British publisher of trade directories.
In 1818 he became the apprentice of James Pigot, a publisher of trade directories.
Pigot died in 1843 and Slater then published directories in his own name.
Due to fierce competition from the firm of Kelly & Co., which in 1845 began expanding to other cities from its home market of London, Slater's company withdrew from the southern England market after 1852 and only published directories for Ireland, Scotland, and northern England.
A majority of its shares were acquired by Kelly & Co. in 1892, although the Kelly name did not appear on the newly acquired directories until years later (not until 1921 in Scotland).