Leonard: Our babies will be smart and beautiful.
Sheldon: Not to mention imaginary.

Leonard: Penny. We are made of particles that have existed since the moment the universe began. I like to think those atoms traveled fourteen billion years through time and space to create us, so that we could be together and make each other whole.

Leonard: Penny, as a scientist, my job is to figure out why things happen. But I don't think I'll ever understand how someone like me could get to be with someone like you. You know maybe I don't need to understand it, I just need to be grateful. I love you, Penny.

Leonard: Oh, I know. This might help. *Gets a ring out of his wallet*
Penny: Where did you get a ring?
Leonard: I've had it for a couple of years. Not important. Penny, will you marry me?
Penny: Oh, my God, yes.
Leonard: This would have been so much more romantic if you didn't have monkey hair on your finger.

Amy: I just read about an experiment designed to see if you can make two people fall in love in a matter of hours.
Leonard: That doesn't sound right. My research has shown it takes three to five years of shameless begging.
Penny: Honey, neither of us comes off good in that story.

Leonard: Before you say anything, have you heard of Schrodinger's cat?
Penny: Actually, I've heard far too much about Schrodinger's cat.
Leonard: Good.
*Leonard and Penny kiss*
Penny: All right, the cat's alive. Let's go to dinner.

Sheldon: Perhaps your talk of my sexual prowess renewed her faith in love.

Penny: God, what is wrong with me.
Leonard: Nothing, you're perfect.
Penny: Gah, I'm not perfect.
Leonard: Yes you are.
Penny: You really think so, don't you? [kisses Leonard]
Leonard: Penny?
Penny: Yeah.
Leonard: How much have you had to drink tonight?
Penny: Just…. a lot.
Leonard: Are you sure that your being drunk, and your being angry with Kurt doesn't have something to do with what's going on here?
Penny: It might. Boy, you're really smart.
Leonard: Yeah, I'm a frickin' genius.

Leonard: I missed you.
Penny: You see me all the time. You sure you don't just miss the sex?
Leonard: Well, yeah, the sex with you is pretty great. Have you ever tried it?
Penny: I have. You're not wrong.

Penny: Okay, I understand everyone's a little tense today, so I am just gonna get to the important stuff. Leonard, standing here with you in front of our family and friends is bringing up a lot of feelings. Like what a good idea it was to elope the first time. But also how incredibly happy you make me. Thank you for marrying me. Hopefully for the last time.

Leonard: Penny, do you have plans for dinner?
Penny: Why, you guys going somewhere?
Leonard: No, just you and me.
Penny: Have you thought this through?
Leonard: Yes, and I think we should go anyway.

Penny: I finally realize I don't need to be famous or have some big career to be happy.
Leonard: Well what do you need?
Penny: You, you stupid Poptart.

Penny: Why can't all guys be like you?
Leonard: Because if all guys were like me the human race couldn't survive.

Penny: Leonard. You're not only the love of my life. You're my best friend. And you've got a friend in me. You got troubles. I got 'em too. There isn't anything I wouldn't do for you. We stick together and we can see it through, because you've got a friend in me.

Penny: You mean like a beta test?
Leonard: Well, technically, this would be an alpha test. A beta test requires people that weren't involved in the development of the appli-
Penny: Seriously, do I not get credit for knowing beta test?
Leonard: No, absolutely you should.

Leonard: It's hard sometimes. Everywhere you go, guys hit on you, even if I'm standing right there. And they're all taller than me. Why is everyone taller than me? You know what, this is all in my head. It's my problem, not yours.
Penny: Leonard, why do you always do this? Listen to me, you're the one I'm with. You know I love you. So will you please relax, because you're driving me crazy.
Leonard: You know that's the first time you ever said you love me.
Penny: Yeah.
Leonard: We're just supposed to pretend it's not a big deal?
Penny: That's exactly what we're gonna do, because you're about to make me cry. And we both know if I start crying, you're gonna start crying.
Leonard: You're right, I should go.

Penny: Leonard, I don’t know what to tell you. It was just a hug.
Leonard: Glad we cleared that up.
Penny: Yeah.
Leonard: I guess I'll see you.
Penny: Okay, have a safe trip.
Leonard: Thank you. Bye.
Penny: Okay, bye. [closes door] It means I wish you weren't going.

Leonard: That's two proposals, one day. Sounds like someone wants to spend the rest of their life telling people how to spell the name Hofstadter.

Leonard: What about if you went out with me?
Penny: Are you asking me out?
Leonard: Um, yes, I am, asking you out.
Penny: Wow.
Leonard: I was just going off your comment about the nice guy...
Penny: No, I know, I got that. Yeah, totally.
Leonard: ...thing and honestly, it's no big deal.
Penny: Yes.
Leonard: Yes what?
Penny: Yes, I will go out with you.
Leonard: Really?
Penny: Yeah. Why not, I mean, what do I have to lose?
Leonard: Yeah. That's the spirit.

Penny: Can I tell you a secret?
Raj: Yeah.
Penny: I screwed up. Leonard's a great guy. Never should have broken up with him.

Leonard: Oh, my God. I'm lying in bed with a beautiful woman who can quote Yoda. I love you, Penny.
Penny: Oh. Oh. Thank you.

Leonard: All right, maybe I overreacted. So we're in two different places emotionally. So what? And maybe I'm a little ahead of you. That's fine. You know. In fact, it makes sense, 'cause let's face it, I've been in this relationship two years longer than you.

Penny: See, that's the kind of passion I didn't think I had. But then I realized I'm passionate about you.
Leonard: Oh, my cute little tushy strikes again.
Penny: No, I'm serious. Look, I've always had these plans. I was gonna be in movies and live this glamorous life, and anything less than that just wasn't worth getting excited about.
Leonard: Those things can still happen.
Penny: Oh, obviously it's gonna happen. Yeah, a psychic at a bachelorette party told me so. Anyway, what I meant was, I shouldn't wait, you know? I've got you, I've got Sheldon, all these wonderful friends. My life is exciting right now.
Leonard: That's a big deal.
Penny: It is, isn't it?
Leonard: So, does that mean we get to do stuff like talk about cool shows or get dressed up in matching costumes and go to Comic-Con?
Penny: Leonard, I had an epiphany, not a stroke.

Leonard: And then a laser will map the reflective surface, and voila. (A floating 3-D image of the pencil appears. Leonard moves it around with his finger)
Penny: Wow. That is amazing.
Leonard: You know, there's a foundational idea in string theory that the whole universe may be a hologram.
Penny: What do you mean? (Leonard flicks a switch. The hologram changes to a view of the planet Earth). Oh, wow!
Leonard: Uh-huh. Well, the holographic principle suggests that what we all experience every day in three dimensions may really (changes projection to the solar system) just be information (changes the projection to the galaxy) on a surface located at the farthest reaches of our cosmos. (Sets the galaxy spinning) So it's possible that our lives are really just acting out a painting on the largest canvas in the universe.
Penny: Hmm.
Leonard: What?
Penny: Sometimes I forget how smart you are.
Leonard: You should visit more often.

Penny: Leonard, you're back.
Leonard: Yeah, I just stopped by to say… [Penny grabs Leonard and kisses him] Yeah, so, hi!
Penny: Hi! [They stumble into her apartment while kissing]

Leonard: Okay, listen to me, this is just a minor setback.
Penny: No, it's not, okay? I've been out here for, like, ten years. I've nothing to show for it.
Leonard: Well, you have me.
Penny: You're right. I do have you. Mm. Let's get married.
Leonard: What?
Penny: Ooh. Leonard Hofstadter, will you marry me?
Leonard: Um…
Penny: Did you seriously just say um?
Leonard: Look, you know I love you but, but you're, you're drunk and sad and feeling lost.
Penny: Okay, so, so you don't want to marry me?
Leonard: That is not what I said.
Penny: No, forget it. I take it back. Offer's off the table.

Penny: Um, I'm free tonight.
Leonard: Are you saying you want to get married?
Penny: Vegas isn't that far away.
Leonard: I'm in. Let's do it.

Leonard: Hey. Listen, since we got, you know, interrupted last night, I didn't have a chance to give you this.
Penny: Oh, Leonard, you shouldn't have. Oh, boy! What is it?
Leonard: It's a snowflake. From the North Pole.
Penny: Are you serious?
Leonard: Uh-huh. It'll last forever. I preserved it in a one percent solution of polyvinyl acetal resin.
Penny: Oh, my God. That's the most romantic thing anyone's ever said to me that I didn't understand.
Leonard: It's actually a pretty simple process. You see, cyanoacrylate are monomers which polymerize on... [Penny kisses him]