The ruby slippers are the shoes worn by Dorothy (played by Judy Garland) in the 1939 MGM movie The Wizard of Oz. Because of their iconic stature, they are now among the most treasured and valuable of film memorabilia. As was customary for important props, a number of pairs were made for the film, though no one knows exactly how many. Five pairs are known to have survived; one of these was stolen in 2005 and never recovered.
In the film, Dorothy's house falls on the Wicked Witch of the East, killing her and freeing the Munchkins from her tyranny. Glinda, the Good Witch of the North magically puts the dead woman's ruby slippers on Dorothy's feet to protect her from the Witch's vengeful sister, the Wicked Witch of the West. Dorothy knows the slippers are magical, but she is unaware of their specific powers. At the end of the film, Glinda reveals one of the slippers' abilities: Dorothy can return home to Kansas by simply clicking her heels three times and repeating, There's no place like home.
It is speculated that at least six or seven pairs of the final design were made; four pairs used in the movie have been accounted for. According to Rhys Thomas in his Los Angeles Times article, they were likely made by Joe Napoli of the Western Costume Company, and not all at once, but as the need arose. This would help explain why they are different sizes; according to Thomas, all the ruby slippers are between Size 5 and 6, varying between B and D widths. 
The Western Costume Company in Hollywood claims to have made Garland's original slippers. While it is likely that Western would have been contracted to make some of The Wizard of Oz's many costumes, no records of the original slippers exist to either validate or disprove their claim. In 1989, to commemorate the movie's 50th anniversary, Western produced the only authorized Ruby Slipper reproductions. Hand-lasted on Judy Garland's original foot mold and completely sequined and jeweled, the reproduction slippers were nearly identical to the originals. Western planned a limited edition of 500 pairs at $5000 each, but halted the project after selling only 16 pairs.