Before reading this article, I advise you to read the article 1997 Laws - Basic.
These are the changes that are not technical ones in my opinion, so they may affect you. The technical ones are in 1997 Laws - Technical.
The definition of Convention is a little strange: it seems to define a natural call as one willing to play there or showing length [at least three cards] or strength in the denomination [even though it does not use the word "natural"], then define a convention as any other call. The full definition is given in 1997 Laws - Technical.
There have been a few arguments about "the footnote to L12C2", which gave Appeals Committees but not Tournament Directors the right to adjust an assigned adjusted score to do equity. Since this did not appear in American Law books, nor in several others around the world, its existence was doubted. It will now appear as a new section, L12C3, but it is a Zonal option. People like myself will be extremely disappointed that it has not been extended to Tournament Directors. There is no other change to adjusted scores, except that an average minus can be less than 40%.
The first major change concerns Unauthorised Information. When a player on the offending side withdraws a call or play, previously his partner was allowed to use such information, after any penalty. In the new Laws, he is not allowed to. Suppose your partner leads out of turn when it is declarer's lead, and before anything else happens, declarer leads himself. Your partner's card can be withdrawn without penalty [L53C]. At the moment you are allowed to use the knowledge that he wanted to make that lead: in the new Laws it is forbidden [L16C2].
Have you ever asked a question about a bid not made? RHO opens 4C, showing hearts, and you ask what a 4H bid would have shown. Bloody-minded players have always tried to avoid answering, because you are not asking about the actual sequence. It has long been a bone of contention. Now you are allowed to ask such a question: it specifically says so in the new L20F1. Incidentally, has anyone ever said that you are not allowed to ask questions about individual bids? Many read L20F1 as saying so, though there has been no attempt to enforce this: the new Law makes it clear that individual questions are permitted.
If you try to change an inadvertent call without pause for thought, the advent of bidding boxes has complicated the time factor. What happens if you only realise you have made the wrong call some time afterwards, when you look down and see it [yes, I have passed my partner's Precision club before now!]? What happens if LHO has called? CHO? RHO? Dummy has appeared? Discussions earlier this year on the bridge-laws mailing list discovered that some allow no changes after LHO has called, and in one case a change was allowed after dummy had appeared! The discussion concluded that until partner called seemed fair, and the new L25A has legalised this.
Unfortunately if you try to change your call too late, or deliberately because you have changed your mind, you use L25B. The same time problems occur: however the Lawmakers have made a very late change, and decided that you may not change after LHO calls. Different countries have had different views as to what the TD should do if someone asks whether they can change their call: the new Laws clearly permits this change.
Much of this very complex Law is unchanged: as previously, a player offers his new call: the next player can accept it. If he doesn't, the player can choose whether to go back to the original call and silence partner, or pick another call [yes, it can be a third call!] This section is unchanged: so far. Now for the new bit: if this last occurs, then the player who changed his call is now playing for a maximum of 40% on the board, although his opponents can get whatever they get. Directors [and Scorers] are going to love this one!
If someone attempts to change an insufficient bid under L25B some countries allow either the insufficient bid or the substituted bid to be accepted: some do not. The ACBL added their own footnote, not in European Law books, so that the insufficient bid could be accepted, but not the substituted bid. In the new L25B1 the footnote appears somewhat altered with the effect of the current ACBL practice, so that only the insufficient bid may be accepted.
Law 26 deals with lead penalties. If a player withdraws a call that shows a suit, then there are no lead penalties if the suit was shown previously or later: formerly this only applied if the suit was specified later.
A simple change to insufficient bids: currently you cannot correct an insufficient conventional bid without incurring a penalty: in future you will not be allowed to correct an insufficient natural bid without incurring a penalty either, if the correction would be to a bid that would normally be conventional. If this is not clear: you bid 1D over 1NT. Currently you may bid 2D without penalty if the 1D is natural: in future you will only be allowed to if both the 1D and the 2D are both natural [L27B1A].
Another one for the bloody-minded: if three cards have been played to a trick and declarer calls for a card from dummy by saying "High" or something, then the defence can no longer insist he wastes a big card: it is assumed that he means the smallest winning card [L46B1].
L47E had a couple of anomalies: if an opponent had given you misinformation you could change your play even if it did not affect you! This is no longer the case. Occasionally you could retract your opening lead after seeing dummy: this also no longer applies. Also if you tell an opponent that it is his lead when it is not he has always been allowed to retract it: it has been noted that you should not accept it!
If the Zonal authority does not allow defenders to ask each other "Having none?" [currently the case in Europe but not North America: L61B has a Zonal option] then the question establishes the revoke through L63A4, a Law that does not appear in ACBL Law books. In the new Laws it becomes L63B: the revoke is not established, ie the player must substitute a legal card, but the penalty is applied as though the revoke is established.
One of the great changes in the 1987 Laws was to introduce the concept of "could have known" so that a Director who suspected some malpractice did not have to produce proof positive that there was no other explanation before giving an adjusted score. He no longer had to say "You are cheating so I am adjusting the score": in some circumstances he could say "You have made a call/play that could have been based on ..., so I am required to adjust, even though you may not have done anything untoward." It appeared in various places such as L23. In the new Laws this above generalised Law now means that the principle applies in every situation.