We build houses ultimately to provide shelter. Regardless of the size or scale of any building or the climate you build in, it is designed pimarily to keep the weather out (be it rain, wind, cold, heat or even bugs and animals) from the environment we have created on the inside.  
 
Log homes are primarily built using green timber, that is, the trees have been recently felled and have not quite reached an equilibrium moisture level, nor have they been naturally or artificially dried ( as in a kiln ). The costs of drying wood to that degree are prohibitive and it's not generally practical. Air drying can take up to 4 years to reach equilibrium and kilns are not generally designed for whole logs.  I suppose when the pioneers built using whatever materials were around, they didn't have time to wait 4 years before their timber dried and they could start building their houses. So, in some cases, building with dry timber wasn't even an option. There are also certain disadvantages to using dry timber such as having to deal with warped, twisted, cracked and brittle logs all of which is a function of the drying process.  
 
Using green timber with appropriate techniques, the generally unavoidable characteristics of drying logs can be minimised or even used to advantage. Green logs are easier to cut with a chainsaw, are easier on tools because the moisture acts as a natural lubricant and are generally straighter and more flexible when wet. Of course green timber logs are much heavier as they are laden with water. However, the traditional techniques for log building have been built around the assumption of using green timber.
 
How do we build a weathertight shell using green timber but have it remain weather tight even after drying, twisting and shrinkage? The way in which the logs are joined at the places where they meet is of the utmost importance and is the key. The ways in which logs have been joined to provide weathertightness is an area which has been at the center of log bulding for centuries. Many techniques abound - many of which have become best practices refined over centuries and handed down from generation to generation. Which is not to say that there has been a convergence on any specific technique or that there isn't still room for improvement. Many regional differences have developed arising from differences in the available materials and/or tools and/or skills.  
 
In the last few decades, with better communication and sharing of techniques as well as scientific study, there have been advances made in the understanding of wood movement. Let's begin with some common facts about working with green wood: