Romance

Romance is possible in Mass Effect and Mass Effect 2 for both male and female characters.

Mass Effect
In Mass Effect, Commander Shepard has the option to pursue heterosexual romantic involvement with a human squad member - Ashley Williams for males and Kaidan Alenko for females - or xenophilic romance for both genders with the asari squad member, Liara T'Soni. Regardless of gender, Shepard can also have a sexual encounter with the asari Consort, Sha'ira.
 * Attraction - When waking after Eden Prime, Shepard will find either Ashley Williams or Kaidan Alenko waiting at the Commander's bedside in the medical room, feeling guilty over getting snagged by the Prothean Beacon. Shepard can be reassuring and claim there was no way to know what the beacon would do, at which point Williams or Alenko will look much happier and a little intrigued.


 * Courting - After completing the first primary mission on each key world - either Therum, Noveria or Feros - Shepard can speak to either Ashley or Kaidan and begin building up a rapport that gradually grows into a romantic interest.


 * "Dr T'Soni?" - Once Liara T'Soni is on board, Shepard can also court her as above after Liara admits looking into Shepard's background. Although temporarily stopped, this rapport can continue after Shepard's second encounter with a beacon through another set of dialog options with Liara. If Shepard has spoken to Liara at all, even platonically, and is already involved with either Kaidan or Ashley, during the next conversation he or she will ask if Shepard is attracted to Liara. Shepard can either express an interest in Liara - which will effectively end the romance path with that squad member - or explain their relationship is only professional.


 * Two's Company, Three's a Crowd (optional) - If Shepard has been wooing Liara and the human love interest at the same time, after the next completed mission on a primary world, the commander will suddenly be confronted by both potential love interests after the debriefing. They will ask Shepard to choose between them. Choosing one will continue that romance and end the other (and no, Shepard can't have both: if the Commander suggests it, the human love interest will leave and the romance will be continued with Liara).


 * Sacrifice - On Virmire, Captain Kirrahe will ask for one of the squad members to join his diversion effort while Shepard infiltrates the base. Both Ashley Williams and Kaidan Alenko will volunteer, and Shepard is forced to choose one of the two potential love interests to risk in the assault. Later, near the end of the mission when Saren attacks, Shepard will be forced to choose which squad member dies in the nuclear blast. Sacrificing Shepard's current love interest will end that romance path.


 * Lockdown - While there's really no time to woo the commander's romantic interest during the pursuit of Saren, they will come to Shepard's side after the argument in the Council Chambers. Only a decisively Renegade conversation path will negatively impact the romance at this point; otherwise the romantic interest will comfort and reassure Shepard. However, the intimate mood is immediately shattered by Joker with an urgent call over the ship's comm.


 * Conclusion - If the romance subplot has been continued, while en route to Ilos the love interest pays a private visit to Shepard's personal quarters aboard the Normandy. Paragon choices will make for a passionate ending and an intimate cut-scene.

Completing the romance subplot unlocks the Paramour special achievement.

Asari Consort
After completion of the assignments associated with the asari Consort, Citadel: Asari Consort dealing with Septimus and Xeltan, and upon returning to the Consort's Chambers, Sha'ira will offer a reward of words, "an affirmation of who you are and who you will become." If the Commander expresses dissatisfaction with the offered reward, Sha'ira will initiate a sexual encounter with Shepard.

Mass Effect 2
Commander Shepard is again able to pursure potential love interests in Mass Effect 2. Males are able to pursue heterosexual romantic involvement with potential squadmate Subject Zero or the SSV Normandy SR-2's Yeoman, Kelly Chambers. It is unknown if either of these potential love interests are available to females, or the full number of potential love interests that are possible for either gender.

If an imported Shepard has a love interest from the original Mass Effect, then that relationship will continue into Mass Effect 2, even though the love interest will be unable to join Shepard's squad. However, it is possible for Shepard to be unfaithful and pursue a relationship with one of Mass Effect 2's potential love interests. 

Trivia
The inclusion of a sex scene in Mass Effect led to some controversy and inaccurate rumours in the mainstream media after its content was misunderstood. An additional message that can be found in Asteroid X57's pirate radio shack (in the PC version of Bring Down the Sky) may be a "response" to this controversy.