Wide Gauge was an early model railway standard, introduced in 1906 by Lionel Corporation. As it was a toy standard, rather than a scale modeling standard, the actual scale of wide gauge locomotives and rolling stock varied. It ran on three-rail track that was 2 1/8 inches (nearly 54 mm) apart.

Lionel dubbed its new standard Standard Gauge and trademarked the name. Other manufacturers, notably Ives and American Flyer, adhered to Lionel's standard and called their compatible offerings Wide Gauge. Lionel's Standard Gauge should not be confused with Standard Gauge for real railroads, or the later S gauge popularized by American Flyer after World War II.

Wide gauge's heyday began in the boom of the 1920s, when high incomes made large toy trains affordable. The scale all but disappeared in the Great Depression, with Ives' bankruptcy in 1931 and American Flyer and Lionel abandoning the scale in 1932 and 1940, respectively, in favor of smaller, more affordable sizes such as O gauge.

In recent years, wide gauge equipment has been produced by a number of smaller manufacturers in limited quantities for the hobbyist market.