  The Advanced Camera for Surveys (ACS) enables low resolution slitless
spectroscopic imaging in the three channels. The most-used modes are grism
imaging with the WFC and the HRC at a resolution of 40 and 24 A/pixel,
respectively. In the far UV there are two prisms for the SBC and a prism for
the HRC in the near-UV. An overview of the slitless spectroscopic modes of the
ACS is presented together with the advantages of slitless spectroscopy from
space. The methods and strategies developed to establish and maintain the
wavelength and flux calibration for the different channels are outlined. Since
many slitless spectra are recorded on one deep exposure, pipeline science
quality extraction of spectra is a necessity. To reduce ACS slitless data, the
aXe spectral extraction software has been developed at the ST-ECF. aXe was
designed to extract large numbers of ACS slitless spectra in an unsupervised
way based on an input catalogue derived from a companion direct image. In order
to handle dithered slitless spectra, drizzle, well-known in the imaging domain,
has been applied. For ACS grism images, the aXedrizzle technique resamples 2D
spectra from individual images to deep, rectified images before extracting the
1D spectra. aXe also provides tools for visual assessment of the extracted
spectra and examples are presented.
