Dick Wolf’s characters on Chicago Fire, Chicago P.D. and Chicago Med are intertwined on a variety of levels, including siblings, marriages and failed romances.

Fans got a taste for the crossover connections within the One Chicago universe early on with Chicago Fire’s Gabby Dawson (Monica Raymund) and Chicago P.D.’s Antonio Dawson (Jon Seda). The fictional sister and brother duo first appeared on screen together during season 1 of Fire, which debuted in 2012.

Fans met another sibling duo with Chicago P.D.’s Jay Halstead (Jesse Lee Soffer) and Chicago Med’s Dr. Will Halstead (Nick Gehlfuss). However, the crossovers between shows isn’t all about siblings: Chicago Fire’s Kelly Severide (Taylor Kinney) dated a Chicago P.D. and a Chicago Med character before finding love on his own series.

Scroll down to see how the One Chicago characters are related — and which crossovers led to romances: