List of ALCO diesel locomotive classes

The American Locomotive Company (ALCO), based in Schenectady, New York, United States produced a wide range of diesel-electric locomotives from its opening in 1901 until it ceased manufacture in 1969. This is a list of ALCO locomotive classes.

For individually notable locomotives, please see List of locomotives. There are numerous individual ALCO locomotives that are preserved in museums or heritage railways. In particular please see sublists List of preserved locomotives in the United States and List of preserved locomotives in Canada.

Century series
ALCO announced its "Century Series" of diesel locomotives in 1963 as a leap forward in power and reliability, an attempt to compete more aggressively with GM-EMD and GE in the marketplace.