As I explained
in a posting in the Forum’s “Getting to Know English” section way back in March 2009, “on behalf” and “in behalf” are both correct usage, and today they tend to be used interchangeably, particularly in American English. But
The American Heritage Book of English Usage cites this traditional rule: use “on behalf of” to mean “as agent of, on the part of,” and use “in behalf” to mean “for the benefit of.” Examples: “Robert accepted the ‘Best Performer’ trophy on behalf of his sister Angela, who was on a European singing tour.” “The Class of ’92 held a benefit concert in behalf of the flood victims.” The two phrases are actually very close in meaning. In my case, I prefer “on behalf of” and will not worry about my choice at all.
