Sead Kolašinac (pronounced [sěad kolaʃîːnats]; born 20 June 1993) is a professional footballer who plays as a centre-back for Serie A club Atalanta. Born in Germany, he plays for the Bosnia and Herzegovina national team.

Kolašinac started his professional career at Schalke 04, playing first in its reserve team, before joining Arsenal in 2017, who loaned him back to Schalke 04 in 2021. The following year, he moved to Marseille. A year later, he signed with Atalanta.

A former German youth international, Kolašinac made his senior international debut for Bosnia and Herzegovina in 2013, earning over 60 caps since. He represented the nation at their first major championship, the 2014 FIFA World Cup.

Kolašinac started playing football at his hometown club Karlsruher SC, which he joined in 2001. In 2009, he moved to TSG Hoffenheim's youth academy. A year later, he switched to VfB Stuttgart's youth setup. In 2011, he went to Schalke 04's youth academy. In June 2012, he signed his first professional contract with the team. He made his professional debut against Greuther Fürth on 15 September at the age of 19.

Kolašinac debuted in the UEFA Champions League away at Montpellier on 4 December.

In June 2013, he extended his deal with the squad until June 2017.

In August 2014, he suffered a severe knee injury, which was diagnosed as an anterior cruciate ligament tear and was ruled out for at least six months. Over seven moths after the injury, on 11 April 2015, he returned to the pitch.

On 13 December, he scored his first professional goal against FC Augsburg.