In this basic course we will review common types of language change at every structural level: phonology, morphology, syntax, and semantics. We will also study how language relationships are determined, how subgroupings are justified, and how protolanguages are reconstructed. Where appropriate, we will talk about recent developments in historical linguistics that involve big data: for example, the use of text corpora in studies of syntactic change and use of lexical databases in the detection of language relationship.