Having gone undefeated in their title-winning run last season, SCG Muang Thong United are favourites to retain the Thai Premier League crown.
However, 2011 champions Buriram United, who finished fourth last season, are determined to regain the title, having finished the 2012 campaign in fourth, 10 points behind the Kirins.
Former champions Chonburi FC and BEC Tero Sasana, who were second and third respectively last season, also look strong and could be title contenders.
Muang Thong, owned by Siam Sport Syndicate, announced last week they would continue to strengthen the team with a budget of about 300 million baht.
Champions SCG Muang Thong United had a memorable 2012, finishing the season undefeated.
Muang Thong striker Teerasil Dangda in action against Jeonbuk Hyundai Motors in midweek.
The Kirins, who also won the TPL title in 2009 and 2010, have already signed several players, including Austria striker Roland Linz, who scored 39 goals in 79 matches for Austria Vienna, and South Korea's Kim Yoo-Jin, from Chinese Super League side Liaoning Whowin.
Sarayuth Chaikamdee has joined BEC Tero Sasana from Bangkok Glass FC.
Because each team can field a maximum three foreigners and an Asian at the same time - it is known as the 'three plus one' rule - Muang Thong have also brought in several Thai players.
Among them are Sarawut Masuk from Chamchuri United, Chainarong Tatong from BB-CU, Visanusak Kaewruang from TOT SC, Naphat Thamrongsupakon from Samut Songkhram and Siwakorn Jakkurprasart.
However, Muang Thong's most lethal player is striker Teerasil Dangda, who completed a two-week training stint with Spanish side Atletico Madrid earlier this year.
"Our aim is to retain the TPL title and win other competitions," Muang Thong deputy chairman Viluck Lothong said.
"We do not only buy players but also develop our own through our academy."
Club director Ronnarit Suewaja added: "We have bought several foreign and Thai players and we may have the strongest side in recent years."
Muang Thong are also determined to have a good run in the AFC Champions League. They got off to a decent start with a 2-2 home draw with South Korea's Jeonbuk Hyundai Motors in midweek and have China's Guangzhou Evergrande and Japan's Urawa Reds in their group.
But Muang Thong's campaign could be affected by the absence of Thailand goalkeeper Kawin Thamstachanan, who will be sidelined with injury for much of the season.
Last season, Buriram were apparently affected by the 'three plus one' rule, which replaced the previous rule, which allowed each team to have five foreigners on the pitch at the same time.
Despite struggling to cope with the new rule, Buriram still managed to win the FA Cup and the League Cup.
The Thunder Castle have lost three African players - forward Franck Ohandza to Bundesliga club Greuther Furth, Ghana striker Frank Acheampong to Belgian league leaders Anderlecht and defender Ekwalla Herman to China's Chongqing Lifan.
One of the busiest clubs in the close-season, Buriram have signed new players from around the world, including Chile's Ramses Bustos.
Other new stars include Spanish duo Osmar Ibanez and Carmelo Gonzalez, Kai Hiranlo of Japan and South Korean Kee Sang Min.
Thai-Swiss Charyl Chappuis is on loan from Swiss club Lugano. He is a Switzerland youth international and was part of the Swiss team that won the 2009 Fifa U17 World Cup after beating hosts Nigeria 1-0 in the final.
Chappuis, 21, has a Thai mother and is eligible to play for Thailand. He has been called up to the Thai national side along with teammates and fellow foreign-born Thais Anthony Ampaipitakwong (US), Dennis Buschening (Germany).
Suree Sukha has moved from Chonburi to join his twin brother Surat at Buriram.
Buriram's another notable signing is Anawin Jujeen from Bangkok Glass.
The Thunder Castle had good results in the run-up to the new TPL season at home and in the AFC Champions League.
They beat Brisbane Roar to reach the AFC Champions League group stages and secured a draw at Japan's Vegalta Sendai in their opening group game.
Last week, Buriram beat Muang Thong 2-0 in the King's Trophy match with new signing Bustos scoring both goals.
The contenders
Chonburi FC are seen as third-favourites to win the title. Indeed, the Sharks may be a better bet than SCG and Buriram as they do not have continental assignments to worry about. Chonburi have added Indonesia midfielder Irfan Bachdim, who is on loan from Persema Malang.
Chonburi have also signed midfielder Kraikitti In-utane from TTM and offered a new two-year contract to 38-year-old midfielder Therdsak Chaiman.
Although Chonburi have signed only a couple of new players, their coach Witthaya Laohakul is confident the Sharks are strong enough to win the title.
"If we fail to win the title, then I should allow other people to try," he said.
Once a powerhouse in Thai football, BEC Tero Sasana have been also-rans in recent years, despite funds from BEC, which runs Channel 3.
BEC were in the headlines late last season when they hired former England manager Sven-Goran Eriksson as technical director.
BEC improved considerably during Eriksson's short spell. However, the team admitted they could not afford the Swede's high salary over a long-term contract.
They have signed striker Sarayuth Chaikamdee from Bangkok Glass to team up with Brazilian forward Cleiton Silva, the league's joint top-scorer - with Teerasil - last term.
Apichate Puttan and Sarif Sainui have joined the Fire Dragons from Buriram United, with other newcomers including Yai Nilwong and Japanese Sho Shimoji.
One of the richest clubs in Thailand, Bangkok Glass have failed to live up to expectations for years.
But this could be their year, with several new players including Japanese Shinnosuke Honda (on loan from Buriram), Suphasek Kaikaew (on loan from Chonburi) and Korakod Wiriyaudomsiri (on loan from BEC).
Other new faces include Phuritad Jarikanon and Australian Goran Subara. Teerathep Winothai remains their first-choice striker.
Osotspa M-150 Saraburi could yet be dark horses with the arrival of Apipoo Sunthornpanavej and Kabfah Boonmatoon.
The newcomers
Ratchaburi FC, Suphanburi FC and Bangkok United have joined the top flight after earning promotion from League One.
Backed by Mitrphol, one of the country's biggest sugar companies, Ratchaburi reached last season's Leauge Cup before losing to Buriram United, partly because they could not field players on loan from Buriram.
The Dragons, who will be playing in their first season in the top tier, have signed Douglas Cardozo from Buriram and Ekapoom Potharungroj from Muang Thong.
Like Ratchaburi, Suphanburi will be making their debut in the elite league. They are backed by the Silpa-archa family, arguably the most influential group in the province.
With Varawuth Silpa-archa, son of former Thai Prime Minister Banharn, their chairman, Suphanburi have signed Iraqi Hussein Alaa Hussein from China's Shenzhen Ruby and Ivory Coast's Bireme Diouf from Samut Songkhram FC.
Bangkok United have made a quick return to the TPL after one season in League One.
With TrueVisions their main sponsor, Bangkok United had about 100 million baht to strengthen the team and were one of the busiest teams in the market, signing Ronnachai Rangsiyo, Prakasit Sangsuk, Pongpipat Kumnuan, Tony Pinho and Mario da Silva.
Under respected coach Sasom Pobprasert, also a commentator for TrueVisions, the Angels may be able to avoid the drop.
The promoted trio may be better bets to stay up than Sumut Songkhram, who are still looking for a major sponsor, Si Sa Ket, who are hit by political problems, Pattaya, Chainat and Songkhla United.
Chilean forward Ramses Bustos, right, has joined Buriram United.
Veteran midfielder Therdsak Chaiman, left, received a new two-year contract from Chonburi FC.