Joanna is the love interest to Sam in the 2003 British romantic comedy, Love Actually and it's 2017 sequel Red Nose Day Actually.
Joanna is an American girl in Sam's class. After Sam's mother (who was also called Joanna) dies, he is left in the care of his stepfather Daniel, who notices that he's been acting depressed even before the death. Sam tells Daniel that he's in love with Joanna, but doesn't know how to woo her. After noticing that rock stars always have girls going after them, Sam decides to start learning the drums in an attempt to impress her.
At the school's Christmas pageant, Sam gets to accompany Joanna as she sings All I Want for Christmas is You by Mariah Carey. Sam's plan to impress Joanna doesn't work as well as he'd hoped as she barely notices him amidst all the other musicians and singers. As Joanna and her family get ready to leave for America, Daniel tells him that he has to confess to her now or regret it forever. Sam arrives as the airport and makes a dash for Joanna, incurring the ire of several security guards along the way. Sam gets to Joanna and tells her he loves her. Joanna admits she's always been attracted to him and gives Sam a kiss before the guards catch up to him. Joanna then leaves for the Christmas holidays, but returns in the new year and starts a relationship with Sam.
Joanna reappears in the 2017 short film Red Nose Day Actually as part of Comic Relief. Set 14 years after the film, it shows that Joanna remained in her relationship with Sam, who moved to America with her for work.
Joanna returns to England with Sam in order to ask Daniel if she could marry Sam, to which Daniel agrees.