American judge, international authority on juvenile delinquency, and reformer of legal procedures concerning offenses by youths and domestic-relations problems. His controversial advocacy of “companionate marriage” was sometimes confused with the “trial marriage” idea of the philosopher Bertrand Russell.

Lindsey was admitted to the Colorado bar in 1894. He wrote the statute establishing a juvenile court in Denver, and from 1900 to 1927 he presided over that tribunal, which was the model for similar courts throughout the United States. He applied the now generally accepted theories that the juvenile offender should be protected as a ward of the court, that treatment of the youth's problem rather than punishment should be the objective, and that equity rather than criminal procedure should be employed. In addition, he secured the passage of contributory delinquency laws against irresponsible parents.

After moving to California, Lindsey was elected judge of the Los Angeles Superior Court in 1934. In that city he helped establish a conciliation court to deal with divorce cases when there was some chance of reconciling the parties; he served as judge of that court from 1939 until his death.

An outspoken foe of political machines, Lindsey was an unsuccessful candidate for governor of Colorado in 1906 and a member of the Progressive (Bull Moose) Party's national committee in 1912. He wrote numerous books, the most widely discussed of which was The Companionate Marriage (1927; with Wainwright Evans), in which he argued for birth control to prevent parenthood until a marriage was solidly established and for divorce by mutual consent (but not if children were involved).