  We present the results from a multiwavelength campaign of GRS 1915+105
performed from 2000 April 16 to 25. This is one of the largest coordinated set
of observations ever performed for this source, covering the wide energy band
in radio (13.3-0.3 cm), near-infrared (J-H-K), X-rays and Gamma-rays (from 1
keV to 10 MeV). During the campaign GRS 1915+105 was predominantly in the
"plateau" (or low/hard) state but sometimes showed soft X-ray oscillations:
before April 20.3, rapid, quasi-periodic (~= 45 min) flare-dip cycles were
observed. The radio flares observed on April 17 shows frequency- dependent peak
delay, consistent with an expansion of synchrotron-emitting region starting at
the transition from the hard-dip to the soft-flare states in X-rays. On the
other hand, infrared flares on April 20 appear to follow (or precede) the
beginning of X-ray oscillations with an inconstant time delay of ~= 5-30 min.
This implies that the infrared emitting region is located far from the black
hole by >~ 10E13 cm, while its size is <~ 10E12 cm constrained from the time
variability. We find a good correlation between the quasi-steady flux level in
the near-infrared band and in the X-ray band. From this we estimate that the
reprocessing of X-rays, probably occurring in the outer parts of the accretion
disk, accounts for about 20-30% of the observed K magnitude in the plateau
state. The OSSE spectrum in the 0.05-10 MeV band is represented by a single
power law with a photon index of 3.1 extending to ~1 MeV with no cutoff. The
power-law slope above ~30 keV is found to be very similar between different
states in spite of large flux variations in soft X-rays, implying that the
electron energy distribution is not affected by the change of the state in the
accretion disk.
