"Finally. I'm really happy to be here", said Aubameyang, according to Arsenal.
Gabon global Aubameyang, 28, played for Dortmund in their 2-2 draw against Freiburg on Saturday but did not score.
He becomes Arsenal's third signing this January, after Konstantinos Mavropanos and Henrikh Mkhitaryan and will link up with his former Dortmund teammate following the arrival of the Armenian from Manchester United earlier this month.
Aubameyang, who scored 98 goals in 144 Bundesliga games for Dortmund, expressed hius delight at the deal and his hope of emulating Arsenal's record goalscorer Thierry Henry. But always I believe that his behaviour has been top, top class.
"I think it's a great thing that you can add two guys coming from two different clubs that already played with each other".
The Belgian was expected to team up with his Chelsea teammates last night ahead of our Premier League clash against Bournemouth at Stamford Bridge tonight.
Giroud feels he has joined one of the biggest clubs in the Premier League in the shape of Chelsea and says he can not wait to get started with the English champions.
A £12m signing from Montpellier in the summer of 2012, he scored 105 goals in 253 appearances for Arsenal in all competitions, winning three FA Cups and three Community Shields.