Each booklet, more than 40 pages long, carries details of the proposed merger and a voting form that has to be returned by 15 May.
First copies were posted this weekend, with further batches to follow over the next two weeks, at an estimated cost of up to £2m.
Members, who receive separate booklets depending on which society they belong to, are being told the merger is an ideal marriage.
"The strength of the Halifax brand will be complemented by the strong product branding of the Leeds, including the Liquid Gold Savings account and the Home Arranger service," Halifax members are being told. Leeds members receive a similar message.
Both societies' members are being encouraged to cast their votes either in the postal ballot or by attending special general meetings in Leeds and Halifax.
If approved by members, the merger must be confirmed by the Building Societies Commission, the industry's regulator, at the end of June. It could take place in August, creating a giant building society valued at up to £10bn.
The next stage, of conversion to a publicly quoted bank - expected to take place in 1997 - will give share handouts to members.