Mozart wrote an astonishing 20 operas during his lifetime. The first, Apollo ed Hyacinthus (K38) was completed in 1768 when Mozart was just 8 years old and he finished the last opera in the final months of his life in 1791. Most of the operas are not performed often and while the music is beautiful the really great works are later on. Mozart's later operas plumb a depth which few later works have achieved, providing political and social commentary as well as a wonderful evening's entertainment.

The operas which are performed regularly are as follows:-

1. Idomeneo K366, first performed at the Court Theatre in Munich in 1781.
2. Die Entfuhrung aus dem Serail K384, first performed at the Burgtheater in Vienna, 1782.
3. Le Nozze Di Figaro K492, first performed in 1786 at the Burgtheater in Vienna.
4. Don Giovanni K527, first performed in 1787 at the Nationaltheater in Prague.
5. Cosi Fan Tutte K588, first performed in 1790 at the Burgtheater in Vienna.
6. La Clemenza Di Tito K621, first performed in 1791 at the Nationaltheater in Prague.
7. Die Zauberflote K620, first performed at the Theater auf der Weiden, Vienna in 1791.

So which Mozart opera should you listen to first? I would consider Le Nozze Di Figaro to be a must for a first Mozart opera. It has a storyline which is somewhat easier to follow than some of the operas and the music is approachable and enjoyable. It is of course in any Mozart opera, but in for example La Clemenza Di Tito some of the arias are rather long and complex. The plot of Figaro is funny and fast moving, involving the characters from Rossini's later opera The Barber of Seville at a later point in their lives. In the story the Count is something of a womanizer, and the whole plot plays on this with some sarcastic political commentary by Beaumarchais, who wrote the play on which the libretto is based. The opera is also about forgiveness. Watch for the moment when the Countess asks the Count to forgive her, and he refuses. Later on, the Count asks the Countess for forgiveness which is granted. Both are great moments in the opera.

Another Mozart opera which works well for your early studies of his works is The Magic Flute (Die Zauberflote), a fantasy story about what happens to Tamino following his encounter with a monster from which he is saved by three mysterious ladies. This one is particularly good for younger viewers as it has pantomimic elements, but also has a more serious side. Mozart became a Freemason in the early 1780s and there are many elements of Freemasonry hidden within the music and plot, which are often brought out in different productions. It's in the Singspiel style with spoken dialogue interspersed in between the dialogue. If you can manage to get hold of the Ingmar Bergman recording available on a DVD produced by Criterion, it's about the best performance of the opera that I have ever seen.