William Le Roy Emmet (July 10, 1859 – September 26, 1941) was an electrical engineer who made major contributions to alternating current power systems including the design of large rotary converters.

Emmet was a leading advocate of the electrical propulsion of ships from turbines.

[3] He also developed the mercury vapour turbine system for electric power production.

[4] He received the AIEE Edison Medal in 1919 For inventions and developments of electrical apparatus and primo movers.

He received the Elliott Cresson Medal of the Franklin Institute in 1920 and was elected to the National Academy of Sciences in 1921.