When a coordinating conjunction connects two or more independent clauses—word groups that could stand alone as separate sentences—a comma must precede the conjunction. There are seven coordinating conjunctions in English: and, but, or, nor, for, so, and yet.

A comma tells readers that one independent clause has come to a close and that another is about to begin.

exception: If the two independent clauses are short and there is no danger of misreading, the comma may be omitted.

tip: As a rule, do not use a comma with a coordinating conjunction that joins only two words, phrases, or subordinate clauses. (See P2-a. See also P1-c for commas with coordinating conjunctions joining three or more elements.)

The word group following and is not an independent clause; it is the second half of a compound predicate (controls...and invests).