This paper presents the first experimental demonstration of femtosecond diffractive imaging using the FLASH soft X-ray free-electron laser (FEL). The study shows that a single diffraction pattern can be recorded from a large macromolecule, virus, or cell before the sample is destroyed by the intense X-ray pulse. The experiment used a 25 fs, 4×10¹³ W/cm² pulse with 10¹² photons at 32 nm wavelength, which produced a coherent diffraction pattern from a nano-structured non-periodic object before destroying it at 60,000 K. A novel X-ray camera was used to record the diffraction pattern with single photon detection sensitivity. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling, shows no measurable damage and extends to diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one. X-ray free-electron lasers (X-ray FELs) are expected to permit diffractive imaging at high resolutions of nanometer- to micrometer-sized objects without the need for crystalline periodicity in the sample. High-resolution structural studies within this size domain are particularly important in materials science, biology, and medicine. Radiation-induced damage and sample movement prevent the accumulation of high-resolution scattering signals for such samples in conventional experiments. Damage is caused by energy deposited into the sample by the very probes used for imaging, e.g., photons, electrons, or neutrons. At X-ray frequencies, inner shell processes dominate the ionisation of the sample; photoemission is followed by Auger or fluorescence emission and shake excitations. The energies of the ejected photoelectrons, Auger electrons, and shake electrons differ from each other, and these electrons are released at different times, but within about ten femtoseconds, following photoabsorption. Thermalisation of the ejected electrons through collisional electron cascades is completed within 10-100 femtoseconds. Heat transport, diffusion and radical reactions take place over some picoseconds to milliseconds. Radiation tolerance in the X-ray beam could be substantially extended, if we could collect diffraction data faster than the relevant damage processes. This approach requires very short and very bright X-ray pulses, such as those expected from short-wavelength free-electron lasers. However, the large amount of energy deposited into the sample by a focused FEL pulse will ultimately turn the sample into a plasma. The question is when exactly would this happen? There are no experiments with X-rays in the relevant time and intensity domains, and our current understanding of photon-material interactions on ultra-short time scales and at high X-ray intensities is, therefore, limited. Computer simulations based on four different models postulate that a near-atomic resolution structure could be obtained by judicious choice of pulse length, intensity and X-ray wavelength,This paper presents the first experimental demonstration of femtosecond diffractive imaging using the FLASH soft X-ray free-electron laser (FEL). The study shows that a single diffraction pattern can be recorded from a large macromolecule, virus, or cell before the sample is destroyed by the intense X-ray pulse. The experiment used a 25 fs, 4×10¹³ W/cm² pulse with 10¹² photons at 32 nm wavelength, which produced a coherent diffraction pattern from a nano-structured non-periodic object before destroying it at 60,000 K. A novel X-ray camera was used to record the diffraction pattern with single photon detection sensitivity. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling, shows no measurable damage and extends to diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one. X-ray free-electron lasers (X-ray FELs) are expected to permit diffractive imaging at high resolutions of nanometer- to micrometer-sized objects without the need for crystalline periodicity in the sample. High-resolution structural studies within this size domain are particularly important in materials science, biology, and medicine. Radiation-induced damage and sample movement prevent the accumulation of high-resolution scattering signals for such samples in conventional experiments. Damage is caused by energy deposited into the sample by the very probes used for imaging, e.g., photons, electrons, or neutrons. At X-ray frequencies, inner shell processes dominate the ionisation of the sample; photoemission is followed by Auger or fluorescence emission and shake excitations. The energies of the ejected photoelectrons, Auger electrons, and shake electrons differ from each other, and these electrons are released at different times, but within about ten femtoseconds, following photoabsorption. Thermalisation of the ejected electrons through collisional electron cascades is completed within 10-100 femtoseconds. Heat transport, diffusion and radical reactions take place over some picoseconds to milliseconds. Radiation tolerance in the X-ray beam could be substantially extended, if we could collect diffraction data faster than the relevant damage processes. This approach requires very short and very bright X-ray pulses, such as those expected from short-wavelength free-electron lasers. However, the large amount of energy deposited into the sample by a focused FEL pulse will ultimately turn the sample into a plasma. The question is when exactly would this happen? There are no experiments with X-rays in the relevant time and intensity domains, and our current understanding of photon-material interactions on ultra-short time scales and at high X-ray intensities is, therefore, limited. Computer simulations based on four different models postulate that a near-atomic resolution structure could be obtained by judicious choice of pulse length, intensity and X-ray wavelength,