I will review the construction of the tensionless limit of string theory, focusing on the work in the last decade. This limit is the diametrically opposite limit of the much more well studied point particle limit, where the length of the fundamental string, instead of shrinking to zero, becomes infinite. The limit is a gateway to the ultra-high energy, ultra-"stringy" sector of string theory. I will discuss the intrinsic formulation of classical tensionless strings based on work by Isberg et al and then how one can understand this in terms of a Carrollian limit on the worldsheet which transforms the residual symmetries from two copies of the Virasoro algebra to the 2d Conformal Carroll algebra indicating that the worldsheet has become a null surface. The classical and quantum aspects of the null tensionless string would be discussed in detail. While the classical strings can be arrived at from both the intrinsic and limiting perspectives, the quantum null strings hold a variety of surprises.
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