Similar to our Solar system, majority of the extra-solar planetary systems also contain multiple planets across several decades in mass and orbital separation. Therefore, knowing the frequency and the internal structure of the multi-planet systems is important toward a correct understanding of planet formation and evolution. In the first part of this talk, I will explain how we reduced the frequency of planetary systems from "more than 50%" to 30% by combining the transit and transit timing variation techniques. Then I will extend the "planet ladder" to larger separation, present the strong correlation between close-in small planets and distant giants, and discuss the implications. In the end, I will switch gear to gravitational microlensing, using (likely) the first pair of microlensing planets near mean-motion resonance to discuss the importance of this technique in the overall planet distribution.