  We report the detection of V1298 Tau b, a warm Jupiter-sized planet ($R_P$ =
0.91 $\pm$ 0.05~ $R_\mathrm{Jup}$, $P = 24.1$ days) transiting a young solar
analog with an estimated age of 23 million years. The star and its planet
belong to Group 29, a young association in the foreground of the Taurus-Auriga
star-forming region. While hot Jupiters have been previously reported around
young stars, those planets are non-transiting and near-term atmospheric
characterization is not feasible. The V1298 Tau system is a compelling target
for follow-up study through transmission spectroscopy and Doppler tomography
owing to the transit depth (0.5\%), host star brightness ($K_s$ = 8.1 mag), and
rapid stellar rotation ($v\sin{i}$ = 23 \kms). Although the planet is
Jupiter-sized, its mass is presently unknown due to high-amplitude radial
velocity jitter. Nevertheless, V1298 Tau b may help constrain formation
scenarios for at least one class of close-in exoplanets, providing a window
into the nascent evolution of planetary interiors and atmospheres.
