When an atom or molecule is exposed to an intense infrared laser pulse, an electron which was released earlier may be driven back by the laser field to recollide with the parent ion. These recollisions incur well-known phenomena such as high-energy photoelectrons and high-order harmonic generation (HHG). In both cases, some features of the structure of the parent ions are imbedded in the observed electron or photon spectra, respectively. With mid-infrared lasers as the driving pulses, I will show that accurate bond length of the molecular ions can be extracted from the observed photoelectron momentum spectra. This is the underlying theory behind the idea of laser-induced electron diffraction (LIED). The LIED has been used to extract the bond length of diatomic molecules (O2 and N2), as well as the C-C and C-H bond length of acetylene (C2H2). We will also show that two-dimensional structure of the molecule, including bond angles, can be retrieved if the molecules are aligned in 1D. I will also introduce how synthesized waves can enhance the diffraction signals in LIED.