Order by related field title I have a series of talks that have speakers as a related entry.

I'm looking for a way to order the talks by the last name of the speaker (the last name is the title of the speaker channel).
You probably have to loop through all the speaker (ordered by lastName) that are related to the talks (the speaker entry is the targetElement). Then use one craft.entries (ElementCriteriaModel) for each loop to get the talk entry.

See this Q/A for a comparable problem.