Just booked our trip to London and Paris!

With just 3 days in Paris, I would not spend one of them on the train.

Rick's London guide book is excellent at giving you a list of popular sights. Many enjoy the Tower of London, Westminster Abbey, St Pauls, National Gallery, Churchill War Rooms, National Portrait Gallery, British Museum, Museum of London, Tate Britain, Tate Modern, perhaps a walk with London Walks.

Rick's Paris guide book is also excellent at giving you a list of things that are available to see in Paris. Most first -timers enjoy the Eiffel Tower (either to go up or just look at it from the ground or a Seine River Cruise), Notre Dame, Ste Chapelle, Louvre, d'Orsay, l'Orangerie, Army Museum/Napoleon's Tomb, Rodin Musuem, Cluny Museum and the list goes on.

What you see will really depend on what your interests are for both London and Paris.

Four and three days? You are going to miss many things. What you should miss depends on what you really want to see and why.

For me the top priorities in London are Saint Paul's (not as thrilled with Westminster Abby), the British Museum, Trafalgar Square and the National Gallery, The Tate Britain (I'm in love with Turner), The Churchill Rooms, and the Imperial War Museum. I could live without Windsor and the changing of the guard and the Tower of London is worth seeing but not on my must see list. We did the Eye last trip and it was fun, but not on my top list. The real question is what kinds of things do you want to see. You can't see all the major sights in four days.

Three days in Paris is a few too few to begin with. I'd stick to Paris. Notre Dame, Sainte Chapelle, The Louvre, and the Effile Tower are obvious. We love the Rodin Museum and the Orsay. We also love the Army Museum. Again, the real question is what kinds of things do you like to see.

It's all rather personal. If I knew your interests I could be more helpful.

Allow some time in both cities to walk through neighborhoods and parks.

With 4 days in London and 3 in Paris, I would probably not plan to take a long day trip to Brussels. Unless you have been many times and already seen a lot...

In Paris, a day out at Versailles would be nice - not nearly as far off as Brussels. I like the fat tire bike tour where you bike through the gardens and have a picnic before going inside the palace. Your other two days would be chock full of things to see in town - Notre Dame (climb the tower to meet the gargoyles up close and personal!), St. Chappelle, the Eiffel tower, the Louvre, the Musee d'Orsay, the Musee Rodin and the Cluny Museum are some of my favorites. You will be exhausted if you fit those into three days, because you also need time to eat pastries and drink wine!

If you really want to add another town, my vote would be for a day trip to Bath from London. We climbed to the top of the church tower, did the walking tour, toured the baths which I found fascinating, and had time for a nice lunch and dinner. In London, the must sees might be the Tower, Westminster Abbey, Churchill's Cabinet War Rooms or the Imperial War Museum if you are interested, the British Museum and a ride on the Thames down to Greenwich. I also liked the Mews to see the carriages right around the corner from the changing of the guard, and there are lots of museums.

With just 7 days for London and Paris you don't have time for other towns.

What are your flight arrival and departure times?
Have you booked Eurostar yet? Time?

Good for you. Eurostar tickets usually go on sale 120 days in advance, so be prepared in January to buy your train tickets to Paris and take advantage of the huge savings.

With such a short time in each city, concentrate on what most interests you. If ancient Greece and Egypt are your thing, go to the British Museum. Many of the best museums in London are free (makes up a little for the high price of rooms). That makes it easy to drop in, see a couple of things and leave . . . or spend hours if you like.

Get a guide book from the library or use the internet to read about the sights and make a list of the ones you are most interested in. Frommer's destination websites have lists of the sights and rate them (0 to 3 stars). Then group them by area (use google maps) - paying attention to opening hours and days. Some sights are open one or more evenings, some sights are closed one day a week. You won't be able to see everything, but you'll have plan. Many people like to start in a new city with a Hop On, Hop Off (HOHO) bus. The routes are usually about 2 hours and go past many of the top sights. They aren't a very good option for hopping on and off since city traffic can slow them down a lot in London and Paris. Another option for Paris is a bike tour with Fat Tire Bikes. They also have Segway tours that are a lot of fun.

Walking tours are a good way to see a part of a city. London Walks are excellent, Paris Walks are usually good, though it depends on the luck of the draw with the guide.

Leave some free time to soak up the atmosphere - pubs in London, cafes in Paris.

I booked my trip to Paris for next May about a month ago, and while some of the joy of the anticipation of it has dimmed a bit I'm still excited and starting to make a stab at an itinerary for my 7 days. I'm a big fan of all museums but plan to visit the ones that really focus on specific art that I love--Picasso, d'Orsay, Pompidou, Rodin, Cluny, and select parts of the Louvre. I love flea markets and vintage stuff so planning to spend Saturday at Les Puces de Saint-Ouen. A day trip to Versailles is the only time I'll venture outside Paris. Also on my list is visiting the Eiffel Tower, Pere Lachaise cemetery, Notre Dame, the Conciergerie, Montmartre, and that's as far as I've gotten--and of course time to just wander. I'm staying in the 6th arr and that's close to Montparnasse. I travel solo and can cover a lot of ground quickly.

With just 3 days in Paris I wouldn't suggest leaving it unless you feel a need to see Versailles.

I visited London 4 years ago and again focused on things that were of great interest to me--#1 was spending Saturday at the Portobello Road market. Next favorite was the Churchill War Rooms and museum, Victoria & Albert, Westminster Abbey, the Tower, British Library, guided day trip to Oxford, Windsor Castle and Stonehenge and a very, very long day trip by train to Edinburgh--this was my first trip abroad and of course now I would have taken the train there and stayed a couple of days then flown home.

While these forums are a great source of helpful advice, nothing takes the place of doing your own research to find out what a country/city has to offer and deciding for yourself what you will be most satisfied seeing and doing.

Eurostar tickets go on sale on the Eurostar UK website 180 days in advance, not 120. Prices start low and rise.

To echo what others have said - if you only have 3 days in Paris to follow 4 in London, I would not advise trying to take in Brussels unless you have been to Paris many times.

As to what 'not to miss' - that really depends on what you enjoy doing. Folks here can help, if you can post a list of things you are considering, and Rick's books are a great place to start if you need ideas. Whatever you decide, do walk in both cities.

Ok our arrival times are as follows:

May 1 - Arrive in London at 10:00am
May 2 - Day in London
May 3 - Day in London
May 4 - Check out and head to Paris (Eurostar booked for 11am) Afternoon in Paris
May 5 - Day in Paris
May 6 - Day in Versailles maybe?
May 7 - Leave Paris 1:30pm

I know this isn't a huge amount of time but it is what we have in vacation time to take.

You may as well go ahead and make plans for your return trip, because what you plan this time is just enough to get you excited about these two great cities!

You essentially only have two full days in either city. Brussels should not come into the picture!!

Make time for what interests you! If you are a big fan of theater, you can get tickets for an evening performance in London. The big shows there are on the same level as Broadway, but are actually a lot cheaper. I love history and castles, so The Tower of London was my favorite spot when I went to London as a kid and it is at the top of my list for my visit in March. The British Museum is another favorite of mine and it's free so I am eager to go back.
Obviously if you are an art lover, the Louvre and Musee D'Orsay house amazing collections, but if you aren't passionate about looking at paintings and statues it might be better to do something else that you do love and not spend the time in the lines and crowds. If you buy tickets to the Eiffel Tower in advance you can save yourself the line wait, and using your time well on a short visit is essential. If you read through a guidebook or look up some lists online and as you are reading them, make your own list of things you think you'd enjoy. I love visiting Cathedrals and several of Paris' big churches are free to visit, as are the big cemeteries. If you are really interested in the history and architecture of Versailles (and you don't mind crowds) then it might be worth one of your Paris days, but, again, only do it if it sounds very interesting to you. It's your trip and you should only spend your trip doing the kinds of things you enjoy, not what everyone else says is the "must see" sights. My tip: Don't eat, buy, or do anything you could find at home :)

No one is mentioning the Houses of Parliament? I am very interested in politics and world events and this was top on my list. I brought my 11 year old son and he really enjoyed seeing this as well. Now when he looks at the news and sees David Cameron speaking, he says "I remember seeing that!" It all depends on what your interests are. I love history so we saw Houses of Parliament, Westminster Abbey, Tower Bridge, Tower of London, Buckingham Palace, London Eye. The Hop On/Hop Off buses are good at giving you an overall view of what London has to offer. I will suggest that you get your tickets ahead of time and print them out. This way you will no have use precious time on paying for admission. I also enjoyed the audio guides that were available at the sights since you were able to view at your own pace and learn so much. I am going back in July to go to all the places that I missed the first time. Three days is not enough. You really need a week to do London properly. I would also try to go to the Borough market. We never had a chance to go, but I am definitely going in July.

Do you love the Impressionists ? I would put the Orangerie on my list (amazing Monet murals of his garden) as well as the Marmatton museum (a little outside the city center, but refreshingly uncrowded) And, in May, some time in the beautiful public gardens.

Brussels is the most boring city I have visited in Europe. Spend your time in Paris. I hope you are flying open jaw as you don't have time to cover London and Paris in much detail, let alone go elsewhere.

London. National Gallery and the adjacent Portrait Gallery then go to Covent Garden and take in an evening concert in St Martins in the Fields and have supper down in the crypt. Natural History Museum and the V&A. St Pauls, the Tower of London and Tower Bridge and Borough Market. Houses of Parliament, Westminster Abbey, Buckingham Palace (don't bother wasting time with the changing of the guard) and St James Park.

Paris. Eiffel tower, Montmartre, Notre Dame, boat trip on the Seine and view the small, dark Mona Lisa in the Louvre.

I like Jennifer's post. Efficient, hits all the high points, but not so crowded as to wear you out. Don't forget to spend plenty of time just walking around and marveling; what Rick calls a "Pinch me, I'm in London/Paris" moment. Have some ale in a London pub, and wine or coffee in a Paris café. Relax and enjoy yourself. You don't have to see it all, nor do you want to. Happy travels!

Just to note that Monet's "Waterlilies" at the Orangerie are on canvas, with the galleries specifically modelled (and remodelled) to display them. http://www.nytimes.com/2006/05/16/arts/design/16oran.html?_r=0

For your 3 days in Paris
Wed May 4
Sacre Coeur & Montmartre
Evening Seine River Cruise vedettesdupontneuf.com
Thu May 5
Saint Chapelle
Notre Dame
Pantheon
Jardin du Luxembourg
Musee d'Orsay (closes 9.45pm Thu)
Fri May 6
Eiffel Tower
Invalides
Walk ... Invalides >> Pont Alexandre III >> Grand+Petit Palais >> Champs Elysees >> Place de la Concorde >> Madeleine >> Opera >> Place Vendome >> Tuileries Gardens >> Orangerie >> Pyramid du Louvre
Louvre (closes 9.45pm Fri)