In the draft they added Jared Sullinger and Fab Melo, who could be the future frontcourt for years to come. Through free agency they replaced Allen with Courtney Lee and former sixth man of the year Jason Terry.
Putting the additions alongside Kevin Garnett, Paul Pierce and Rajon Rondo, this looks like a team ready to make another run at the championship.
With the roster nearly set, it comes down to adding some minimum-salary players to help fill out the bench. They are in need of another guard as well as another big man down low, and you can never have too many shooters.
Here are some of the best from the summer leagues that maybe the Celtics should keep their eyes on.
At 28, Leon Powe is not the player you expect to find playing in the summer league.
He played 70 games during the 2008-2009 season but has only played in 50 games since then. He sat out all of last season and played for the Chicago Bulls this summer.
His best outing this summer came against Houston, when he totaled nine points and six rebounds. He finished the summer averaging 4.6 points and 3.6 rebounds in five games.
Powe knows the Celtics and might be a good guy to help fill out the bench. He could help mentor rookies Jared Sullinger and Fab Melo, while being the fifth big man.
Like I said with Powe, you don't find many 28-year-olds with NBA experience playing in the summer league. However, here is another one in former College Player of the Year, Adam Morrison.
Morrison hasn't played in the league since 2010, when he was part of the World Champion Lakers team. Since then, he has been playing overseas.
For the Nets he averaged a little over five points per game, while with the Clippers averaged 20 points and shot over 60 percent from three-point land.
Just like Powe, Morrison suffered a torn ACL and really hasn't been the same since. While he has failed to live up to the hype of his college career, maybe he could find a role on the Celtics as a sharpshooter.
If you are looking for someone with a little more upside and without the medical red flags, then Malcolm Thomas might be just what you are looking for.
Thomas, like Powe, played for the Bulls' summer league and played well. He averaged a double-double in the summer league with 11.4 points and 12.4 rebounds in five games.
He went undrafted last season and bounced between the D-League teams for the Lakers, Spurs and Rockets. Thomas actually started the season last year in China, where he averaged 21 points and 11 rebounds before being released from his contract.
If there was a summer league last season, Thomas probably would have been picked up then. But because there wasn't, he has fallen through the cracks. He could provide some much-needed defensive help in the way of shot blocking.
In just two seasons at San Diego State he became their all-time leading shot blocker. Letting him learn from Kevin Garnett could be a perfect situation for both him and the Celtics.
While Doc Rivers has missed out on coaching his son Austin, maybe he'd be okay with coaching another coach's son.
At 29, Coby Karl, is the oldest player on this list but comes without the injury concerns. His career was detoured mostly do to cancer.
He went undrafted out of Boise State but managed to make the Lakers roster his rookie year. Since then he has bounced around the NBA, D-League and overseas play.
He could provide a sharpshooter off the bench and back up the newly-acquired Courtney Lee until Avery Bradley returns.
With Avery Bradley injured, the Celtics don't have a backup for Rajon Rondo on the roster besides sixth man Jason Terry.
Look no further then Scott Machado, who went undrafted out of Iona. After setting the school record in assists he was named a finalist for both the Bob Cousy and Wooden awards.
During his senior season he averaged 13.6 points and 9.9 assists. He also shot 40.5 percent from beyond the arc and 49.5 percent overall from the field.
At 6'1", he is the same height as Rondo and they are both incredibly quick. In Machado they find a great backup or perhaps even an eventual replacement for Rondo.
Having Rondo, Terry and Machado would give coach Doc Rivers some very quick guards to work with.
I just wonder, as a Knicks fan, if Machado could put on that Boston green every night.