  In this paper we present the null string origin of the ambitwistor string.
Classically, the null string is the tensionless limit of string theory, and so
too is the Ambitwistor string. Both have as constraint algebra the Galilean
Conformal Algebra in two dimensions. But something interesting happens in the
quantum theory since there is an ambiguity in quantizing the null string. We
show that, given a particular choice of quantization scheme and a particular
gauge, the null string coincides with the ambitwistor string both classically
and quantum mechanically. We also show that the same holds for the spinning
versions of the null string and Ambitwistor string. With these results we
clarify the relationship between the Ambitwistor string, the null string, the
usual string and the Hohm-Siegel-Zwiebach theory.
