My husband and I are considering a day trip to Windsor from London. Can someone give us advice on the best way to do this? I see from other threads that we could leave from the Paddington or Waterloo stations. Do we need to buy tickets in advance? Once in Windsor, can we go to Oxford on our way back to London? What's the best way to do that?

Thanks again for the help! I really appreciate it!

Oxford is not on the way from Windsor to London. Plus Windsor takes most of the day to visit from London so there wouldn't be time to visit Oxford.

You don't need to buy tickets in advance. Waterloo to Windsor Riverside station is a direct train w/o changes. For Paddington trains, you change at Slough and end up at Windsor central station. Riverside station is a longer walk from the castle, but the train ride is w/o changes - so really 6 of 1/half dozen of the other. Mainly depends on where in London you are starting from.

The important thing to consider, when you're buying your train ticket to Windsor, is whether you want to buy roundtrip or single. Roundtrip tickets are almost always cheaper than 2 one-ways. However, note that the trains serving the two stations are run by separate rail lines. If you buy a r/t ticket from Waterloo -> Windsor Riverside, you HAVE to come back from Windsor Riverside. You cannot use your r/t ticket on a return train from Windsor Central -> Paddington. And Vice Versa.

Oxford itself easily takes up one whole day. I was there last year from 9am -> 6pm and still didn't get to see everything I wanted to.

I agree about Oxford; i'd also just add that you might want to consider taking the direct bus from London (I think it goes from Waterloo) as it drops you more centrally in Oxford than getting the train. There are a few different bus companies, just give it a google.

The "direct bus" from London to Oxford actually departs from Victoria - between the Victoria train station and Victoria coach station. The bus also makes stops at Marble Arch & Notting Hill Gate. The 2 companies I know of are Oxford Tube and Oxford Espress.