This dissertation focuses on reliable communication over point-to-point and multiple access channels with interference, where the interference is unknown to the transmitter or the receiver but is known to a third party whom we call the "helper." The task of the helper is to use his knowledge to significantly improve the quality of the channel, i.e., enable communication at much higher rates than would be possible in the absence of such a helper. For an additive white Gaussian noise (AWGN) channel with an additive interference of arbitrarily high power, we show that in the presence of a helper, who can add his signal to the channel output, it is possible to achieve the capacity of the standard AWGN channel, provided the helper has power that exceeds the sum of the transmitter power and the noise power on the channel. We detail lattice coding strategies for this channel. We also consider discrete memoryless state-dependent channels where there exists a helper who is the sole party in the communication setup having knowledge of the channel state. We devise coding schemes for such channels. We extend these lattice coding schemes to Gaussian multiple access channels with additive interference where one or more encoders has knowledge of the interference.