The triangular numbers were first studied by ancient Greek mathematicians. This chapter discusses novel oddities and observations, harmonic triples of triangular numbers, and special triangular numbers like palindromic, reversible, Smith, Harshad, happy, Kaprekar, abundant, deficient, and exclusionary triangular numbers. The latest results about magic squares containing triangular numbers and the existence of infinite families of triangular numbers containing only odd digits are discussed. Interesting results for the sum and difference of triangular numbers, triangular numbers’ connection to the Golden Ratio, π, and Pythagorean triples and factorials are also discussed.