Time-reversal symmetry is a defining property for photons and phonons propagating in linear stationary media. While such linearity is advantageous from a design perspective, it leaves us vulnerable to many detrimental effects arising from disorder and defects both at the material level and at the system level. In fact, it is necessary to break time-reversal symmetry to produce important protective devices like isolators and circulators. This talk will describe how traveling wave interactions can be leveraged in photonic devices for producing strong symmetry breaking effects, with particular attention on acousto-optic and electro-optic methods. We then discuss how these approaches can help solve scaling challenges for photonic integrated circuits, especially in support of low-temperature quantum technologies and atom-photonic integrated systems. We present experimental demonstrations of record-setting integrated optical isolators without magneto-optics, how magneto-optic Faraday rotation can be emulated in other systems, and how the broader class of non-reciprocal behaviors can be used to enable robust devices that are immune to undesirable scattering and defects.