Here is the ALEC mission as stated on their website.
Our MissionThe mission of the American Legislative Exchange Council is...
...to advance the Jeffersonian principles of free markets, limited government, federalism, and individual liberty, through a nonpartisan public-private partnership of America's state legislators, members of the private sector, the federal government, and general public.
...to promote these principles by developing policies that ensure the powers of government are derived from, and assigned to, first the People, then the States, and finally, the Federal Government.
...to enlist state legislators from all parties and members of the private sector who share ALEC's mission.
...to conduct a policy making program that unites members of the public and private sectors in a dynamic partnership to support research, policy development, and dissemination activities.
...to prepare the next generation of political leadership through educational programs that promote the principles of Jeffersonian democracy, which are necessary for a free society.
Here is a short video featuring author Cliff Schecter where he explains ALEC and how it works.
For more information, see "ALEC Exposed" in The Nation and this piece from the Center For Media and Democracy.