(a) A match shall be one or two innings for each side according to agreement reached before the match.
(b) It may be agreed to limit any innings to a number of overs or to a period of time. If such an agreement is made then
(i) in a one innings match a similar agreement shall apply to both innings.
(ii) in a two innings match similar agreements shall apply to
either the first innings of each side
or the second innings of each side
or both innings of each side.
For both one innings and two innings matches, the agreement must also include criteria for determining the result when neither of Laws 21.1 (A Win - two innings match) or 21.2 (A Win - one innings match) applies.
2. Alternate innings
In a two innings match each side shall take their innings alternately except in the cases provided for in Law 13 (The follow-on) or in Law 14.2 (Forfeiture of an innings).
3. Completed innings
A side’s innings is to be considered as completed if
(a) the side is all out
or (b) at the fall of a wicket or the retirement of a batsman, further balls remain to be bowled but no further batsman is available to come in
or (c) the captain declares the innings closed
or (d) the captain forfeits the innings
or (e) in the case of an agreement under 1(b) above,
either (i) the prescribed number of overs has been bowled
or (ii) the prescribed time has expired as appropriate.
4. The toss
Video: An explanation of the 2010 change to Law 12
Laws of cricket changes - The toss
The captains shall toss for the choice of innings, on the field of play and in the presence of one or both of the umpires, not earlier than 30 minutes, nor later than 15 minutes before the scheduled or any rescheduled time for the match to start. Note, however, the provisions of Law 1.3 (Captain).
5. Decision to be notified
As soon as the toss is completed, the captain of the side winning the toss shall notify the opposing captain and the umpires of his decision to bat or to field. Once notified, the decision cannot be changed.