Martina "Marti" Venturi is a fictional character in Life with Derek, played by Canadian actress Ariel Waller. Life with Derek is a Canadian-produced show, which airs on Family in Canada, and on the Disney Channel in the U.S.

She is considered (and considers herself) the baby of the family, until the 4th season episode "Surprise", when Nora & George announce that they are expecting a baby. She is sweet and thinks she's very innocent, as shown in many of the first episodes. Being the youngest, she often feels left out of the secrets in the family, as she also demonstrated in the episode "Surprise". She has dark brown hair and brown eyes, and has developed and established her own unique style of clothing (and eating habits too).

She once camped out on her bedroom floor in a tent, and pretended she was a dog under the kitchen table in one of the original episodes. A headstrong and stubborn character, she is like a budding version of oldest brother, Derek Venturi. She demonstrates her boldness and pranking techniques in one of the earlier episodes of the show.