Earning a berth in the NCAA tournament is difficult. Stringing those appearances together is even more demanding.

Consider this: Since the NCAA tournament began in 1939 as a tidy eight-team affair, only 20 Division I programs made the field for 10 consecutive years. A pair of powerhouses -- UCLA and Duke -- had two streaks of at least a decade, making a total of 22 10-year streaks.

As we discussed earlier this week, No. 2 Kansas is on the fast track to reach its 27th consecutive tournament in March, and tie North Carolina (1975-2001) for the all-time record. Arizona made its own terrific run, reaching 25 in a row from 1985-2009.

From one perspective, programs are enjoying unprecedented consistency these days. Altogether, five of the nine longest streaks in tournament history are active, though some could end soon.

Let's take a historical glance at the longest active NCAA tournament streaks.

1. Kansas (26)

Larry Brown and Danny Manning drove the Jayhawks to the 1988 national championship. Brown departed to coach in the pros following the season and a longtime North Carolina assistant named Roy Williams took over one of the sport’s premier programs.

Kansas missed the NCAAs in Williams’ first season, but the next year Kevin Pritchard and Mark Randall led a 30-5 team that began what will soon be a record-tying streak. Williams guided Kansas to three Final Fours before heading home to Chapel Hill in 2003.

Bill Self has kept the train rolling. Kansas has reached two Final Fours, and won the 2008 national championship. With four players averaging in double figures and a top 20 offense and defense, No. 2 Kansas should contend for a No. 1 seed come March.

2. Duke (20)

Mike Krzyzewski is the only coach with two streaks of 10 years or longer. His first one ended in 1995, when recovery from back surgery forced him to step down and the Blue Devils plummeted to a 13-18 record. Krzyzewski returned the next year and started another NCAA streak at Duke.

Since, he’s led the program to five Final Fours and three more national championships, bringing his total to five as he continues his 36th season as the Duke coach.

Along the way, Krzyzewski became the NCAA tournament career victories leader (88) and needs one more Final Four appearance to tie the legendary John Wooden at 13.

A defense ranked 155th in points allowed per possession means these Blue Devils aren’t likely national title contenders, but their NCAA streak will likely grow by one.

3. Michigan State (18)

Tom Izzo assumed command in East Lansing prior to the 1995-96 season, replacing his boss Jud Heathcote. The first two seasons didn’t go as planned. The Spartans had a combined record of 33-28 and were spectators rather than participants when March Madness arrived.

Those dark days didn’t last long.

Now Izzo’s name is synonymous with postseason success. He has a 46-17 NCAA championship.

Of course, the Spartans are unbeaten and No. 1 in the polls this season, making them a smart choice to make another deep run in the bracket.

4t. Gonzaga (17)

How’s this for a coaching career? In 16 seasons as the top man in Spokane, coach Mark Few has reached the NCAA tournament every year and never won fewer than 23 games.

He’s won the West Coast Conference automatic bid 12 times and compiled a 448-106 overall record.

The Zags’ impressive NCAA tournament streak actually started in 1999, when Few was an assistant to Dan Monson. That team won 28 games and reached the Elite 8. Monson headed to Minnesota and Few slid over one seat and elevated the program well beyond mid-major status as he made Gonzaga a perennial player on the national scene (The Zags have been ranked in the AP Top 20 in every season since 2001-02).  

With frontcourt forces Kyle Wiltjer and Domantas Sabonis combining for 38 points and 18 rebounds per game, Gonzaga is off to a 9-3 start this season and the West Coast favorite yet again.

4t. Wisconsin (17)

From the inception of the NCAA tournament in 1939 until 1998, a span of 60 years, Wisconsin made the field four times. Granted, the Badgers clipped the nets in 1940 (assuming teams and players actually did that back then). Regardless, for a long time hoops were an afterthought in the lovely college town of Madison, Wisc.

Those feelings began to change in 1999 under coach Dick Bennett and accelerated rapidly once Bo Ryan took over in 2002 and built the program into a consistent force, known for deliberate yet efficient offense and tough, physical defense.

Ryan recorded a 25-14 NCAA record and the Badgers peaked by appearing in the last two Final Fours, losing a close game to Duke in the championship game last April. Ryan stepped down earlier this month, though and an 8-5 squad looks shaky at the moment.

6. Louisville (9)

One legend replaced another when Rick Pitino succeeded Denny Crum prior to the 2001-02 season.

The Cardinals were excluded from the festivities in 2006, but have been on quite the roll ever since, reaching three Elite 8s, two Final Fours and winning the 2013 national championship in a great battle with Michigan.  

Louisville won at least 30 games in four of those seasons, and Pitino (53-18 career NCAA tournament record) has reloaded again.

7. Ohio State (7)

The Buckeyes have a long, rich tradition in basketball that spans the decades, covering greats such as Jerry Lucas and John Havlicek to Jim Jackson and Jared Sullinger.

In its current run of NCAA tournament appearances, Ohio State has reached two Final Fours and an Elite 8.

Yet, the Buckeyes must produce a strong run through the Big Ten regular season or miss the NCAA field for the third time in coach Thad Matta’s 12 seasons.

8. San Diego State (6)

Let us take a minute to appreciate coach Steve Fisher, who turned 70 last March.

Before Fisher showed up, the Aztecs had played in only three NCAA tournaments since joining Division I in 1971. And they had lost in the first round each time.

Now they’ve won six NCAA tournament games, reached a Sweet 16 and have the eighth longest current active streak of appearances. Games at Viejas Arena routinely sell out and the Aztecs have helped boost the profile of the Mountain West Conference.

A rough nonconference run means the streak could easily end in March.