Fluidic devices and methods associated with mixing of fluids in fluidic devices are provided. In some embodiments, a method may involve the mixing of two or more fluids in a channel segment of a fluidic device. The fluids may be in the form of, for example, at least first, second and third fluid plugs, composed of first, second, and third fluids, respectively. The second fluid may be immiscible with the first and third fluids. In certain embodiments, the fluid plugs may be flowed in series in the channel segment, e.g., in linear order, causing the first and third fluids to mix without the use of active components such as mixers. The mixing of fluids in a channel segment as described herein may allow for improved performance and simplification in the design and operations of fluidic devices that rely on mixing of fluids.