Lyman Judson Gage (June 28, 1836 – January 26, 1927) was an American financier who served as the 42nd United States Secretary of the Treasury in the cabinets of William McKinley and Theodore Roosevelt.

In 1853 he moved to Chicago, served for three years as bookkeeper, and in 1858 entered the Merchants Loan and Trust Company, where he was cashier in 1861–1868.

Afterwards he became successively assistant cashier, vice-president, and president of the First National Bank of Chicago, one of the strongest financial institutions in the Midwestern United States.

His administration of the treasury department, through a more than ordinarily trying period, was marked by a conservative policy, looking toward the strengthening of the gold standard, the securing of greater flexibility in the currency, and a more perfect adjustment of the relations between the government and the National banks.

In 1906, Gage indulged his longtime interest in metaphysical phenomena by purchasing property on and subsequently living at Lomaland, a Theosophist retreat in Southern California.

Though this came as something of a shock to the American public, those who knew him privately were not surprised, as Gage had previously studied spiritualism, astrology, and prophesied the death of his own brother through a "psychic flash".