行星际磁场（IMF）是指存在于太阳系行星际空间的磁场。

因为太阳风是等离子体，它有着磁流体力学的特征，而不是单纯的气体。例如，它是良好的导电体，所以来自太阳的磁力线会随着太阳风一起运动。太阳风的动态压力主导着磁压几乎通过整个太阳系（或太阳圈），所以磁场会因为向外的运动和太阳自转的结合，由于太阳自转，磁力线呈螺旋状，在黄道面上，被拉扯形成阿基米德螺线的形式（派克螺旋）。

行星际磁场具有扇形结构，在每个扇形内部，磁场方向指向或背离太阳是一致的，而两个相邻扇形内磁场的极向却是相反的。

依据半球和太阳周期的相位，磁场的螺旋会向内或向外：磁场在太阳圈的南部和北部的螺旋有着一致的形状，但是方向是相异的。这两个磁域由一分为二的电流片分隔着（电流被限制在一个弯曲的平面内），这个太阳圈电流片有着与芭蕾舞者裙摆相似的形状，在形状上的变化会随着太阳磁场大约11年的反转周期而改变。

The interplanetary magnetic field (IMF) is the solar magnetic field carried by the solar wind among the planets of the Solar System.

Since the solar wind is a plasma, it has the characteristics of a plasma, rather than a simple gas. For example, it is highly electrically conductive so that magnetic field lines from the Sun are carried along with the wind. The dynamic pressure of the wind dominates over the magnetic pressure through most of the Solar System (or heliosphere), so that the magnetic field is pulled into an Archimedean spiral pattern (the Parker spiral) by the combination of the outward motion and the Sun's rotation. Depending on the hemisphere and phase of the solar cycle, the magnetic field spirals inward or outward; the magnetic field follows the same shape of spiral in the northern and southern parts of the heliosphere, but with opposite field direction. These two magnetic domains are separated by a two current sheet (an electric current that is confined to a curved plane). This heliospheric current sheet has a shape similar to a twirled ballerina skirt, and changes in shape through the solar cycle as the Sun's magnetic field reverses about every 11 years.