With back-to-back trips to the Super Bowl, it’s fair to say that the conference once ruled by Tom Brady and Peyton Manning now belongs to Patrick Mahomes and the Kansas City Chiefs.

But last season’s churn lifted new contenders and stoked new rivalries that could define the next decade for the A.F.C. The Buffalo Bills reached the conference championship and the Cleveland Browns won a playoff game, both for the first time since 1994, and the two franchises are looking to build on that success. Meanwhile, the Baltimore Ravens and Tennessee Titans will try to settle their disdain for each other without drawing newly emphasized taunting penalties this season.

Though the Texans’ fate is wrapped up in Deshaun Watson’s future, rookie quarterbacks will have their say elsewhere as the Jaguars’ Trevor Lawrence, Jets’ Zach Wilson and Patriots’ Mac Jones make their debuts. Here’s a look at where the A.F.C. stands as the 2021 season kicks off.

A.F.C. East

Buffalo Bills (13-3)

Key additions: QB Mitchell Trubisky, WR Emmanuel Sanders, RB Matt Breida

Key departures: WR John Brown, CB Josh Norman

The Bills came within one game of returning to the Super Bowl last season, so their priority was to lock in their best talent, starting with quarterback Josh Allen, who signed a six-year contract extension during training camp. To round out what were the N.F.L.’s second-best offense and a middling defense in 2020, the team also re-signed linebacker Matt Milano, guard Jon Feliciano and offensive tackle Daryl Williams, and picked up the fifth-year option on linebacker Tremaine Edmunds, and restocked the offensive and defensive lines early in the draft.

Miami Dolphins (10-6)

Key additions: WR Will Fuller V, QB Jacoby Brissett, CB Justin Coleman, RB Malcolm Brown

Key departures: LB Kyle Van Noy, QB Ryan Fitzpatrick

The Dolphins were one of the most improved teams in the N.F.L. in 2020, bouncing back from a five-win 2019 season to narrowly miss a playoff berth. To get over the postseason hump, the team gave quarterback Tua Tagovailoa another deep threat in Fuller, to go with DeVante Parker and Jaylen Waddle, whom the Dolphins drafted sixth overall. Tagovailoa went 6-3 in nine starts, with 11 touchdowns last season, so there’s reason to expect improvement, but if he falters, Brissett’s one-year deal gives the Dolphins a veteran to step in to lead an offense that ranked 22nd in the league last year.

New England Patriots (7-9)

Key additions: QB Mac Jones, TE Jonnu Smith, TE Hunter Henry, WR Nelson Agholor

Key departures: QB Cam Newton, RB Sony Michel, S Patrick Chung, OG Joe Thuney

Bill Belichick doesn’t like losing and after experiencing his first losing season since 2000, the year he took over in New England, the Patriots’ coach had a very busy off-season. Quarterback Cam Newton clearly was not the long-term solution to the hole left by Tom Brady, but the rookie Jones will face an expedited development after Newton’s sudden release at the end of training camp.

Jones benefits from Belichick’s free agent spending in the off-season, when the coach used the league’s second-most cap space to lure in elite tight ends Smith and Henry, who figure to factor heavily in the offense. Defensive back Jalen Mills and linebacker Matthew Judon, who spent five seasons with the Baltimore Ravens, round out the summer haul that should alert Buffalo and Miami that Belichick wants his division back.

New York Jets (2-14)

Key additions: QB Zach Wilson, WR Corey Davis, DT Sheldon Rankins, DE Carl Lawson

Key departures: LB Jordan Jenkins, LB Tarell Basham, WR Breshad Perriman

After a disastrous 2020 season, the Jets and their new head coach, Robert Saleh, need more than just one off-season to fill all the holes in their roster. They began the restock in April’s draft by selecting Wilson, who takes over what was the league’s worst offense, and targeting the secondary by taking five defensive backs, led by Jamien Sherwood of Auburn.

Davis and Keelan Cole Sr. should provide receiver depth alongside Jamison Crowder, and running back Tevin Coleman, who arrives in free agency after playing in only eight games for the 49ers last season due to a knee injury, should give Wilson a release valve if he’s healthy.

A.F.C. North

Baltimore Ravens (11-5)

Key additions: WR Sammy Watkins, LT Alejandro Villanueva

Key departures: RB Mark Ingram II, LB Matthew Judon, DE Yannick Ngakoue

By their standards, the Ravens had a down year in 2020 despite finishing 11-5 in one of the league’s most competitive divisions. Opponents found ways to slow the team’s running game and quarterback Lamar Jackson, whose season ended with a concussion sustained during the divisional round loss to the Buffalo Bills.

Jackson enters his fourth season no doubt motivated to show why he deserves a big long-term contract extension and Watkins’ deep threat potential should help him make his case. He will also need to adjust to the absence of J.K. Dobbins, the lead running back who suffered a season-ending knee injury during a preseason game, though the Ravens have a capable backup in Gus Edwards.

Team executives aiming for a deeper postseason run focused as usual on defense, re-signing linebackers Chris Board, Tyus Bowser and L.J. Fort, to go with a talented backfield that includes Marcus Peters and Marlon Humphrey.

Cincinnati Bengals (4-11-1)

Key additions: WR Ja’Marr Chase, RT Riley Reiff, CB Eli Apple, CB Ricardo Allen

Key departures: WR A.J. Green, RB Giovani Bernard

Quarterback Joe Burrow, the first overall draft pick in 2020, saw his disappointing rookie season end in Week 11 when he tore ligaments in his left knee on a brutal hit. Burrow is expected to be back for the season opener against Minnesota, behind an improved offensive line coached by Frank Pollack, who returns to Cincinnati after two seasons with the Jets.

Though the team passed over Penei Sewell to reunite Burrow with Chase, who should again give his quarterback a reliable deep threat, it added Reiff to the line on a one-year deal and drafted Jackson Carman, who protected Trevor Lawrence at Clemson, in the second round. Those additions likely won’t be enough to stop the Browns, Ravens and Steelers from continuing to dominate the division, but they’ll suffice if they keep Burrow off the operating table.

Cleveland Browns (11-5)

Key additions: DE Jadeveon Clowney, CB Greg Newsome, S John Johnson, LB Anthony Walker

Key departures: DT Sheldon Richardson

After ending the N.F.L.’s longest playoff drought with a wild card win over the vaunted Steelers, the Browns aren’t settling for a victory lap in the 2021 season. General Manger Andrew Berry continued revamping the roster this off-season, with a square aim on a defense that allowed too many clock-sucking drives in 2020.

Berry brought in the top available defensive free agent in April, signing Clowney to a one-year deal to complement Myles Garrett in the pass rush, and added Johnson, perhaps the best available secondary player in free agency. Baker Mayfield, who cut down his turnovers in 2020, should benefit from having a healthy Odell Beckham Jr. to target.

Pittsburgh Steelers (12-4)

Key additions: RB Najee Harris, DB Miles Killebrew, OT Joe Haeg

Key departures: RB James Conner, C Maurkice Pouncey, LB Bud Dupree, T Alejandro Villanueva

The Ben Roethlisberger era, now in its 18th season, persists. How it will end is the question. Big Ben, 39, seemed to toss off any questions about his rebuilt throwing arm by beginning last season on an 11-0 run. But Pittsburgh couldn’t complete a rally in the wild card round to beat the Browns and the season was dashed well shy of expectations.

The Steelers re-signed one of Roethlisberger’s favorite receivers, JuJu Smith-Schuster, and drafted in the first round running back Najee Harris, who broke Derrick Henry’s rushing touchdowns record at Alabama. But the Steelers lost two of their best offensive linemen and with Cleveland on the rise and Baltimore looking for a longer playoff run, the Steelers will have a hard time winning the A.F.C. North again.

A.F.C. South

Houston Texans (4-12)

Key arrivals: QB Tyrod Taylor, RB Rex Burkhead, OT Marcus Cannon, OL Justin Britt

Key departures: WR Will Fuller V, C Nick Martin, DE J.J. Watt

The 22 pending lawsuits against Deshaun Watson accusing him of sexual misconduct, which he has denied, loom over a franchise that chooses to pretend it’s not at all weird for him to take fourth-team reps at quarterback or serve as scout-team safety — or be with the team at all. Then again, not much makes sense about the Texans, whose front-office dysfunction and salary-cap mismanagement alienated their best players and precipitated a roster, reconstituted with free agents on short-term deals and coached by a first-timer in David Culley, that may luck its way into a victory or two. Or maybe not.

Indianapolis Colts (11-5)

Key arrivals: QB Carson Wentz, OT Eric Fisher, DT Antwaun Woods, DE Kwity Paye

Key departures: QB Philip Rivers, QB Jacoby Brissett, OT Anthony Castonzo, DE Denico Autry, LB Justin Houston, S Malik Hooker

Not many teams are constructed and coached as well as the Colts, who went about solving the quarterback quandary prompted by Philip Rivers’s retirement … by acquiring one of the worst in the N.F.L by many statistical measures, advanced or traditional. Carson Wentz has been reunited with Coach Frank Reich and Press Taylor, former mentors in Philadelphia, but is recovering from foot surgery that imperils his availability for Week 1. If Wentz can’t revive his career, a team brimming with talent — guard Quenton Nelson, defensive tackle DeForest Buckner and linebacker Darius Leonard all rank among the best in the league at their positions — can expect to struggle, especially with a brutal early schedule.

Jacksonville Jaguars (1-15)

Key arrivals: QB Trevor Lawrence, RB Carlos Hyde, DT Malcom Brown, CB Shaquill Griffin

Key departures: WR Keelan Cole

In a college hotbed, owner Shahid Khan has entrusted a successful college coach, Urban Meyer, and the best college quarterback prospect in a decade to resuscitate one of the N.F.L.’s woebegone franchises. The Jaguars will be relevant. Whether they’ll be anything more than competitive depends on the progress of, duh, Lawrence, and their brigade of recent high draft picks, defensive end K’Lavon Chaisson, cornerback C.J. Henderson and receiver Laviska Shenault. Alas, the Jaguars couldn’t schedule Florida A&M or Kent State to ease Meyer’s transition; they’ll have to settle for playing the Texans twice.

Tennessee Titans (11-5)

Key arrivals: WR Julio Jones, DE Denico Autry, LB Bud Dupree, CB Caleb Farley

Key departures: WR Corey Davis, TE Jonnu Smith, LB Jadeveon Clowney, CB Malcolm Butler

The Titans were perhaps the most unbalanced team in the N.F.L. last season — elite offense, woeful defense — and hey, guess what? They very well might be again. Their off-season makeover yielded an inexperienced secondary and a thin group of pass-rushers headlined by Dupree, who is coming off knee surgery.

It also netted Jones, who if he stays healthy adds another mismatch in the passing game to complement A.J. Brown. As assembled, the Titans are good enough to win this middling division again, but their chances would improve if they narrowed that gap between offense and defense even a bit.

A.F.C. West

Denver Broncos (5-11)

Key Additions: QB Teddy Bridgewater, CB Patrick Surtain II (1st round) CB Ronald Darby, CB Kyle Fuller

Key Departures: RB Phillip Lindsay, CB A.J. Bouye, TE Nick Vannett, RT Ja’Wuan James

The Broncos spent much of training camp evaluating a quarterback battle between a journeyman and a young, inconsistent passer.

Teddy Bridgewater, discarded by the Carolina Panthers in a trade, wrenched the starting job away from Drew Lock, who led the league in interceptions thrown in 2020. Bridgewater’s risk-averse play should be a boon to receivers Jerry Jeudy and Courtland Sutton. Star linebacker Von Miller returns from an ankle injury that kept him out last season, holding down a strong defense that got better for drafting cornerback Patrick Surtain II and adding the veteran Fuller in free agency.

Kansas City Chiefs (14-2)

Key Additions: OT Orlando Brown, OG Joe Thuney, DT Jarran Reed, OL Austin Blythe

Key Departures: OT Eric Fisher, WR Sammy Watkins, OT Mitchell Schwartz

The Chiefs’ depleted offensive line was exposed in last year’s playoffs, first when Mahomes took on a hit by the Browns in the divisional round, and definitively in the Super Bowl, when the Buccaneers sacked Mahomes twice and hit him nine times. General manager Brett Veach addressed the deficiency in the off-season by trading for Brown and drafting 6-foot-5 center Creed Humphrey in the second round. The new-look offensive line should give Mahomes the time in the pocket to find his speedy playmakers instead of relying on him to be one.

Las Vegas Raiders (8-8)

Key Additions: DL Yannick Ngakoue, RB Kenyan Drake, WR John Brown, OL Alex Leatherwood

Key Departures: WR Nelson Agholor, DE Takkarist McKinley, RB Devontae Booker

Tight end Darren Waller became the Raiders’ best offensive weapon last season, catching 107 passes and posting over 1,000 receiving yards. Opponents noticed. This season, defenses focused on stopping Waller should be kept honest by running back Josh Jacobs, who earned his first Pro Bowl selection in 2020, and deep threat receiver Henry Ruggs III.

The Raiders’ top-10 offense was weighed down by a defense that ranked 30th in the N.F.L. and gave up 389 yards per game. New defensive coordinator Gus Bradley was brought in along with Ngakoue, who should compliment Maxx Crosby on the defensive line. That unit could hold control over how hot Coach Jon Gruden’s seat gets.

Los Angeles Chargers (7-9)

Key Additions: C Corey Linsley, OT Matt Feiler, TE Jared Cook, OT Rashawn Slater

Key Departures: TE Hunter Henry, CB Casey Hayward, DE Melvin Ingram

Had a team physician not accidentally punctured Tyrod Taylor’s lung, Justin Herbert may never have played last season. But he did, and his stellar performance — throwing for over 4,000 yards, 31 touchdowns and just 10 interceptions, earned him the Offensive Rookie of the Year Award. Herbert’s rise was the bright spot in a season in which the Chargers clumsily lost seven games by one score and fired Coach Anthony Lynn.

His replacement, Brandon Staley, takes over a revamped offensive line and gets back safety Derwin James, an All-Pro in 2018, who missed 11 games after fracturing his right foot in 2019 and sat out the 2020 season with a torn meniscus. With James healthy, a wild-card berth isn’t out of the question.