2015 British Open field: Jordan Spieth, Tiger Woods headline qualifiers at St. Andrews

The Open Championship is the oldest major in golf, but the overhauled method of constructing its field is just two years old. The Open Qualifying Series, which started in November of last year, is a combination of pro tournaments from across the globe and final "open" qualifying sites across Britain.

The U.S. Open whittles some 10,000 qualifying hopefuls into the 65 or so players for its field largely on one big day of sectional qualifying at sites across the United States. The British Open, on the other hand, will take just 12 players through its open qualifying process. These are the lesser-known players and dreamers, while the rest of the field -- the more famous tour pros -- earn their way through the typical world rankings and past performance exemptions.

The field is 156 players deep, the same size of the U.S. Open and PGA Championship. That's as big as it gets in golf. The Masters does things its own way with the green jackets beholden to different stuffy traditions, one of which is taking every effort to ensure the field remains exclusive and below 100 players. The 156-man field can become a logistical challenge at these majors, but The Open usually has the easiest time of handling it. There's ample sunlight in Scotland and England this time of year, so much that the R&A doesn't even need to use split tees like the other two majors with the same field. Instead, everyone goes off No. 1 in some 10 hours of rolling tee times. Sunrise is around 4:45 a.m. and it stays light out well past 10 p.m.

This year's field has already subbed in a handful of alternates after a series of withdrawals. Chris Kirk broke his hand playing with his kids on his farm. Tim Clark could not navigate South Africa's strict new visa laws in time to get to St. Andrews. And then there was the biggest loss of all, world No. 1 Rory McIlroy ripping up his ankle playing soccer. McIlroy is the first player since Ben Hogan in 1954 not to defend his Claret Jug and just the third world No. 1 to miss a major. The course suited Rory perfectly but Russell Knox, a local Scot, gets his spot.

Let's review the 156-man field and just how the R&A builds it. Each player will be listed under the first method he earned entry in accordance with the 40 different ways to get in the field -- e.g. Jordan Spieth qualified five different ways, but his name shows up just once in the first of the Open's 40 ordered exemptions.

Past Champions

Winning The Open does not come with the lifetime invite like the Masters, but it's pretty close. If you're under 60, you will have a spot. And thankfully for that, we get to keep watching John Daly, the 1995 winner at St. Andrews, take his cuts in a major championship. Former winners who declined to play include Nick Price, Ian Baker-Finch and Greg Norman (along with McIlroy, who had no choice).

There's a separate exemption for the 60-and-over crowd that's almost never used. If you have won The Open, and are still contending at 60-plus years of age, you get a five-year exemption. Tom Watson nearly pulled off the most stunning major win in the history of golf in 2009 at Turnberry, where he was one stroke away from a sixth Claret Jug at age 59. That top-10 finish, however, earned him five more years at The Open. That exemption runs out this week and St. Andrews is expected to be the final Open for the championship's dominant five-time winner.

Top 10 from Last Year

All the majors reward the contenders from the previous year. At Royal Liverpool, Rory McIlroy held a comfortable multi-shot cushion for most of the weekend. But there was still that group behind him battling for a coveted early exemption to St. Andrews. Marc Leishman and Edoardo Molinari both relied solely on this exemption to get in the field.

World Rankings Stars

The biggest chunk of the field comes in through the world rankings points system. Getting over that top 50 threshold is always valuable and triggers exemptions into almost every significant event. The world rankings are also where The Open goes to fill out the final few open spots to get to 156 players in the last few weeks, and also to pick many of the alternates. For example, Richie Ramsay, the most recent alternate to get in with Clark's withdrawal, is 81st in the world rankings. So while it's officially listed as the top 50, the players plucked from the rankings go a bit deeper than that.

Euro Tour and PGA Tour Playoffs Contenders

World rankings points are the best to have, but accumulating FedExCup points and Race to Dubai points also generate plenty of perks. The FedExCup is the PGA Tour's postseason system and the Race to Dubai is the European Tour equivalent. There are four separate exemptions based on those two playoff points systems, rewarding success from last year as well as this season.

Recent major winners

All the majors recognize recent winners of the other three majors as well as champions at the so-called "fifth majors" of the PGA Tour and European Tour. Winning the Masters, U.S. Open and PGA triggers a five-year exemption into The Open -- all four have that same reward. Jason Dufner is the only recent major winner that relied on that exemption, cashing in on that 2013 PGA Championship at Oak Hill. Everyone else was already in the field via previously listed exemption.

In addition to the four majors, The Players Championship and the Euro Tour's BMW PGA Championship, the two flagship events on the two main world tours, also hold an elevated place. The winners of those two events get a three-year exemption to the majors. Only two recent BMW PGA winners needed that exemption.

World tour winners

The Open is often the most international major, and the R&A sets aside several exemptions for the most accomplished players from some of the lesser-known world tours.

Amateurs

The first three majors of the season all open up several spots for different amateur winners from around the world. The Masters tends to hold the amateur player in the highest regard, an antiquated nod to founder Bobby Jones, the greatest amateur. Four players this week will play St. Andrews and be ineligible to win prize money.

Seniors

The U.S. Open, British Open and PGA all reserve a spot for the prior year's winner of the Senior version of that tournament. Bernhard Langer is the best player on the senior circuit in recent years and he won last year's Senior Open at 18-under ... the next closest guy was 5-under.

Qualifiers

As I noted above, The Open has far fewer spots for those long-shot qualifiers (this year's Cinderella is a factory worker) who play their way through the different rounds of local, regional and final qualifying. Instead, this Qualifying Series hands out spots in the field at several different pro events from Australia to South Africa to the PGA and Euro Tours.

There are 10 different pro events, including the last three on the PGA Tour leading into this week, that have Open spots available. Tom Gillis, who lost to Jordan Spieth in a playoff on Sunday at the John Deere Classic, was the last player in the field via the Qualifying Series. And unlike the U.S. Open, the alternates don't come from the guys who came close at the qualifying sites, but rather the aforementioned world rankings. So these are your entrants who played their way in via qualifying: