We report on optical , near-infrared and centimeter radio observations of GRB 000418 which allow us to follow the evolution of the afterglow from 2 to 200 days after the \gamma -ray burst .
In modeling these broad-band data , we find that an isotropic explosion in a constant density medium is unable to simultaneously fit both the radio and optical data .
However , a jet-like outflow with an opening angle of 10-20 ^ { \circ } provides a good description of the data .
The evidence in favor of a jet interpretation is based on the behavior of the radio light curves , since the expected jet break is masked at optical wavelengths by the light of the host galaxy .
We also find evidence for extinction , presumably arising from within the host galaxy , with A ^ { host } _ { V } =0.4 mag , and host flux densities of F _ { R } = 1.1 \mu Jy and F _ { K } = 1.7 \mu Jy .
These values supercede previous work on this burst due to the availability of a broad-band data set allowing a global fitting approach .
A model in which the GRB explodes into a wind-stratified circumburst medium can not be ruled out by these data .
However , in examining a sample of other bursts ( e.g .
GRB 990510 , GRB 000301C ) we favor the jet interpretation for GRB 000418 .