This paper discusses coronal and interplanetary magnetic field models, including static and dynamical aspects. The seminal work of Parker [1958> led to an Archimedian spiral field geometry in the interplanetary medium. The early coronal and interplanetary magnetic field models were static models developed to deal with the lack of magnetic field observations throughout most of the heliosphere. Since we are still in this deplorable state, with a particular lack of observations in the inner corona, these static models are still being run since they enable the field throughout the heliosphere to be estimated with only photospheric measurements. By now extending the static models into the temporal domain, a better understanding of the field line dynamics is just beginning to emerge. This understanding is needed to calculate cosmic ray properties, as well as other dynamic events, such as coronal mass ejections. Presently, a number of poorly understood aspects of the coronal field exist: the overall large-scale field structure, the magnetic field winding angle, and rotational properties of the corona and photosphere. This last topic relates to changing magnetic field patterns. We provide a new paradigm involving streak lines for a better understanding of interplanetary field line behavior. The concept of streak lines was developed for understanding fluid dynamics. Use of this concept may lead to future developments and possible prediction of coronal mass ejections, helping us understand some of the causes of space weather. ¿ 2001 American Geophysical Union