In Getreidegasse no. 9, is where the Leopold Mozart family lived from 1747 to 1773. Wolfgang Amadeus Mozart was born here on January 27, 1756. Today the rooms once occupied by the Mozart family house a museum. The most famous exhibits include Mozart's childhood violin, his concert violin, his clavichord, the pianoforte, portraits and correspondence of the Mozart family.

The International Mozart Foundation first set up a museum in Mozart's birthplace, Getreidegasse 9, on June 15, 1880. During the last few decades the museum was systematically renovated by the International Mozarteum Foundation and has become a cultural site attracting thousands of visitors from around the world to Salzburg year after year.
The Mozart family lived on the third floor of the "Hagenauer House" for 26 years. The house was named after its owner and Mozart's friend, the merchant and grocer Johann Lorenz Hagenauer (1712 - 1792), and consisted of a kitchen, a small chamber, a living room, bedroom and study. On exhibit in the historical rooms are manuscripts (facsimiles), documents and souvenirs, the original portraits of the family members such as the 1789 unfinished oil painting by Mozart's brother-in-law, Joseph Lange of "Mozart at the Piano" and the historical instruments (Mozart's concert piano, clavichord, Mozart's concert and child's violin, viola) that were acquired from Mozart's widow, Constanze Nissen (1762 - 1842) and her sons, Carl Thomas (1784 - 1858) and Franz Xaver Wolfgang (1791 - 1844) by the International Mozarteum Foundation.

In 1994 the Mozart Residence was carefully renovated and reorganized by the Viennese architect, Prof. Elsa Prochazka, according to state of the art museum technology to protect the exhibits from damage.
In 1985 the apartment of Mozart's neighbor, Babette von Moll, the aunt of the famous Salzburg geologist and natural scientist, Karl Ehrembert von Moll (1760 - 1838) located in the rear part of the house facing University Square, was redecorated with private funds into a "commoner's apartment in Salzburg in Mozart's time". In addition to furniture and everyday utensils three themes are documented: "Mozart and the University of Salzburg", "Mozart's friendship to Salzburg families" and "Sacred music and reverence of the saints".

The second floor is dedicated to the theme "Mozart at the Theater". Numerous diorams (miniature stages) illustrate the history of the reception of Mozart's operas. Stage sets from the late 18th to the 20th century display the many different interpretations of Mozart's works. Since 1981, the International Mozarteum Foundation has presented different "Mozart" exhibitions on the first floor of Mozart's Birthplace each year

Source from :http://www.salzburg-visitorscenter.com/information/mozartbirth.htm

The square is dominated by the statue of Mozart by Ludwig Schwanthaler, ceremoniously unveiled on September 5, 1842 in the presence of Mozart's sons. Mozart's widow, Constanze von Nissen, did not live to see the unveiling. She died on March 6th of the same year in the house at Mozartplatz 8. A plaque was placed on the house in her memory.

"Michl march, Mozart is here!" This was the local vernacular when the site for the erection of the Wolfgang Amadeus Mozart monument was being discussed. The two squares coming into consideration were the Hannibalplatz in front of Mozart's Residence (today's Makart Square) and the Michaelsplatz (today's Mozart Square), whose fountain with the Baroque statue of St. Michael had to give way to the Mozart monument."

The Bavarian king, Ludwig I, was an important promotor. He personally contributed a significant amount of money and also donated the marble pedestal, now owned by the Carolino Augusteum Museum. Originally, the monument was to have been unveiled in 1841 but a valuable Roman mosaic tile floor was discovered during excavation work:

"hic habitat [felicitas], nihil intret mali"
(Hier wohnt [das Glück], nichts Schlimmes trete ein),
which postponed the unveiling until September 1842.

Today the so-called "Antretter House", located on Mozart Square 4, accommodates the Salzburg University's Institute of Music. The county chancellor and royal war councillor Johann Ernst von Antretter and his wife Maria Anna Elisabeth bought the house in September 1765. The Antretter family was closely acquainted with the Mozart family, e.g. Cajetan, one of the Antretter's sons and the Mozarts were members of the Bölzl infantry and one of the Antretter daughters was a member of Nannerl Mozart's "scholars". The Antretter family also commissioned Mozart to compose the "Antretter Serenade" K. 185. Numerous letters and diary entries document the friendship between the two families. The attractive building, built between the 16th and 18th centuries, is well worth seeing.

The "Schaffner House" on the adjacent Waagplatz is the birthplace of the poet Georg Trakl.

Source from: http://www.salzburg-visitorscenter.com/information/mozartsquare.htm