The initial season saw 28 teams competing in what can be best described as an "informal" conference. No scheduling criteria existed, schools played whomever they wished. The standings were irrelevant, since a selection committee decided the eight participants in the tournament. The varying schedule strengths, resulting in a de facto division of the conference, meant the selection of only the "stronger" teams to the tournament, regardless of record.
After 3 seasons of 20 plus teams, the ECAC took the logical step and formally split the conference in two, with the strong teams and all the Ivy League schools forming a smaller Division 1 conference. However, the tournament field would continue to be selected by a committee and scheduling was still haphazard. The tournament selections would be abolished starting with the 1971 tournament. The scheduling situation was not resolved until 1982.
The late '60s and early '70s were perhaps the golden age of ECAC Hockey. Cornell, under Ned Harkness, became a powerhouse in the late '60s, winning the NCAA Championship twice (1967 and 1970). Boston University followed with consecutive wins in 1971 & 72 (and a later win in 1978). For five consecutive seasons (1970-74), the NCAA Tournament was held in the east, at Lake Placid, Syracuse and Boston (3 times), a situation never seen again.
The membership did not remain constant over this period. New Hampshire jumped up to D1 in 1966, Pennsylvania did the same in 1967. Army left for D2 in 1973 and Vermont came up to D1 in 1974. Pennsylvania dropped their program in 1978 and Maine joined D1 in 1979.
ECAC Division 1 split into 3 divisions in 1979. The Ivies were one, Boston University, Boston College, Maine, Providence, Northeastern and New Hampshire formed the East group, and Colgate, Clarkson, Vermont, St. Lawrence and Rensselaer formed the West region. Starting in 1982, every school played each member of its region twice, all others once, resulting in an uneven number of games played. The Ivy and East regions played 21 games, the West region 20. Each region winner was given a home berth in the tournament, with the best second place team being the fourth home seed.
1983 saw a major change in the ECAC and Eastern hockey. The entire East Region decided to break away and form a new conference, in response to a potential Ivy breakaway. After the teams formally left in 1984, Army rejoined the conference as the twelfth member, playing a half-schedule. Rensselaer would gain the ECAC a measure of revenge in defeating Providence in the 1985 NCAA Championship game. Army would begin a full schedule starting with the 1986-87 season, the first time in history the ECAC would play a balanced schedule.
Since then, four items of interest have occurred. Harvard won the NCAA Championship in 1989. The playoff structure was expanded from eight to ten teams in 1990. Union replaced Army as a member in 1991 and the ECAC Championships were moved to Lake Placid in 1993, after 31 years in Boston. They would remain there until 2003, when Albany became the new host for the championships and also the headquarters for the conference in 2004, when the hockey administration broke away from the main ECAC structure. The most recent change in structure occurred in 2005, when Vermont departed the ECAC for Hockey East, opening a spot in the conference for Quinnipiac.
