The rules of cricket
Law 12 (Innings)
1. Number of innings
(a) A match shall be one or two innings of each side according to agreement reached before the match.
(b) It may be agreed to limit any innings to a number of overs or by a period of time. If such an agreement is made then
(i) in a one innings match it shall apply to both innings.
(ii) in a two innings match it shall apply to
either the first innings of each side
or the second innings of each side
or both innings of each side.
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 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, 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.
4. The toss
The captains shall toss for the choice of innings on the field of play 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
The captain of the side winning the toss shall notify the opposing captain of his decision to bat or to field, not later than 10 minutes before the scheduled or any rescheduled time for the match to start. Once notified the decision may not be altered.