Free agency has yet to begin, but the Vikings have already been one of the NFL's busiest teams so far this offseason. The past few days have been especially busy as the Vikings look to improve their roster under new Head Coach Mike Zimmer.

Here's a look at a few of the key moves so far…

Move: Re-Signed Everson GriffenPotential Impact:Provides a game-changing pass rusher for Mike Zimmer's new defenseBackground:When attempting to build a roster that can compete for the long-term, it's wise to pay players for what they can do, not for what they've already done. In agreeing to a long-term, big-money deal with Griffen while respectfully parting ways with Jared Allen this offseason, that's exactly what the Vikings have done with their right defensive end spot.

Move:Re-Signed Matt CasselPotential Impact:Secures a veteran who can A) start and win games (5-4 in games in which he played last season) and B) help a young quarterback develop.
Background:Earlier in the offseason, Cassel opted out of his 2014 contract with the Vikings in favor of testing the open market. After Cassel took a quick look, he and the Vikings got together on another contract that will keep him in Purple for at least another season. As stated in this week's Monday Morning Mailbag, I wouldn't read into this as an indictment from the Vikings on the group of quarterbacks in this year's draft. Rather, this puts the Vikings in a position of strength when it comes to potentially selecting one of the quarterbacks because now they don't face the pressure of finding a guy who can start from Day 1.

Move:Re-Signed Larry Dean, Marcus Sherels
Potential Impact:Helps maintain one of the League's top special teams groups.Background:Sherels ranked second in the NFL with a 15.2-yard punt return average (that was also a franchise record) and Dean has finished second in special teams stops in each of the past two seasons. Dean and Sherels can provide depth on defense, too, and while neither would be categorized as a "difference maker" on defense, the fact that they are standout special teams as well as depth guys on defense speaks to their overall value on the roster.

Move:Parted Ways with John Carlson, Letroy GuionPotential Impact:Creates cap space, opportunity for younger playersBackground: Both Carlson and Guion had productive times with the Vikings and may help other teams going forward (Carlson has already signed with Arizona), but now the vacancies created by each of them creates an opportunity for the Vikings to get younger and better in both spots.