The engaged duo have hightailed it to Los Cabos, Mexico, for a sizzling summer getaway, and, a source tells E! News, it looks like the handsome couple are taking full advantage of the vacay's luxe offerings and romantic vibe.
Not to mention enjoying the company of their travel buddies: Aniston and Theroux are joined on the trip by pal Jason Bateman (who costarred with Aniston in Horrible Bosses) and his wife, Amanda Anka.
We're told that the two couples have rented an oceanfront home on the beach near San Jose Del Cabo, where they kicked back and soaked up the summer sun.
"Jennifer and Justin were lying on chaise lounges next to each other and then went swimming together. They were kissing passionately and seemed very much in love," our source says.
Aniston clearly got the royal treatment from her attentive fiancé.
"When Jennifer wanted to get out of the water, Justin went and got a towel for her and then held it up for her and wrapped her up," the eyewitnesses said. "He was doting on her and very chivalrous. They were never far from each other and clearly wanted to spend all of their time together."
At one point, "Jen and Justin swam to the edge of the pool and talked to Amanda and Jason, who were sitting on chairs," our source adds, noting that "Jennifer spent all day tanning by the pool with Justin, Jason and Amanda."
"Jennifer was sipping on SmartWater and listening to music," we're told. "The group had lots to talk about and seemed very relaxed together. Jason and Justin were talking while Jen and Amanda were laughing together. They had a butler coming by and serving drinks. [Jennifer] also had a drink with a lime in it."
The trip also allowed Aniston to break out her fave bikini: The 44-year-old actress was spotted flaunting her enviable figure in a red top and sarong.
And if the breezy ensemble looked familiar, that's because the getup is turning out to be Aniston's go-to poolside look: She was spotted wearing the same number during her trip with Theroux, 42, to Mexico last December...which also happened to be in Cabo San Lucas.
Hey, why mess with a good thing?