Before the beginning of the series, three OVAs were produced for the sole purpose of introducing the characters. The first two were released on DVD bundled with two drama CDs, with the third being sold separately. It is unknown if these will ever be released outside of Japan. 
The first OVA is a re-enactment of the first chapter, where Negi first learns of his job as a teacher and is introduced to the students of Mahora Academy 2-A. It ends with profiles of the Baka Rangers (Asuna, Makie, Yue, Ku Fei and Kaede) as well as Ayaka. Asuna is the only girl in the class that doesn't have romantic feelings for Negi. 
The second OVA is a re-enactment of the "love potion" incident of chapter 2, with profiles at the end of Nodoka, Konoka, the cheerleaders (Misa, Madoka, Sakurako) as well as Kazumi. 
The third OVA is a re-enactment of chapter 13: Negi's Mahora tour with the Narutaki twins. The tour shows Negi to several of the students (Yuna, Akira, Chao, Satsuki, Satomi, Chizuru, Natsumi, Zazie) as well as others that he ends up missing (Sayo, Evangeline, Chachamaru, Chisame, Misora, Ako). After being chewed out by Haruna for completely skipping her, a final scene introduces Setsuna and Mana, keeping watch from something on campus. 
(Source: Wikipedia)

Mahou Sensei Negima! Introduction Film