Swiss German (Schweizerdeutsch, Schwyzerdütsch, Schwiizertüütsch, Schwizertitsch) is any of the Alemannic dialects spoken in Switzerland. Occasionally, the Alemannic dialects spoken in other countries are called Swiss German as well, especially the dialects of Liechtenstein which are closely associated to Switzerland's.
Linguistically, Swiss German forms no unity. The linguistic division of Alemannic is rather into Low, High and Highest Alemannic, varieties of all of which are spoken both inside and outside of Switzerland. The reason "Swiss German" dialects constitute a special group is their almost unrestricted use as a spoken language in practically all situations of daily life, whereas the use of the Alemannic dialects in the other countries is restricted or even endangered.
The dialects of Swiss German must not be confused with Swiss Standard German, the variety of standard German used in Switzerland. Even though Swiss Standard German is influenced by the Swiss German dialects to a certain degree, it is very distinct and any native speaker will immediately note the difference.
There are a few practical books and small dictionaries with direct English to Swiss German translation and can occasionally be found in the bookstores in Switzerland. There are a few more comprehensive books and dictionaries that translate some of the major Swiss dialects into standard German. However, almost any Swiss German speaker will be able to speak standard German or even some English when necessary. For longer stays it may be better to try to learn the native dialect as most conversations between people will be in this unless there are Germans or Austrians involved in the conversation in which case the Swiss will usually switch to accommodate them.
The Italians put Swiss German (Svizzero-Tedesco) into a slightly larger group (Tedesco Alemanno) which encompasses the speech in parts of Southern Germany and the Alsace region in France. Within specifically Swiss German (Svizzero-Tedesco) they break it down generally to West Swiss German and East Swiss German as well as the "highest" German from the mountainous cantons, and also Basel German and Zurich German are in separate categories.

Use
Swiss German is a regional or political umbrella term, not a linguistic unity. For all dialects, there are idioms spoken outside Switzerland that are more closely related to them than some Swiss German dialects. The main linguistic divisions within Swiss German are those of Low, High and Highest Alemannic. Low Alemannic is only spoken in the northernmost parts of Switzerland, in Basel and around Lake Constance. High Alemannic is spoken in most of the Swiss plateau, and is divided in an eastern and a western group. Highest Alemannic is spoken in the Alps.
Each dialect is separable in numerous local sub-dialects, sometimes down to a resolution of individual villages. Speaking the dialect is an important part of regional, cantonal and national identity. In the more urban areas of the Swiss plateau, regional differences are fading due to increasing mobility, and a growing population of non-Alemannic descent. Despite the varied dialects, the Swiss can still understand one another (although on occasion just barely) but may particularly have trouble understanding Walliser dialects.

Low Alemannic

• Basel German in Basel (BS), closely related to Alsatian
  High Alemannic
  
  
  
  • eastern
    
    
    
    • Zürich German, in Zürich (ZH)
      dialects of St. Gallen (SG)
      dialects of Appenzell (AP)
      dialects of Thurgau (TG)
      dialects of Schaffhausen (SH)
      dialects of parts of Graubünden (GR)
      western
      
      
      
      • Bernese German, in the Swiss plateau parts of Bern (BE)
        dialects of Aargau (AG)
        dialects of Solothurn (SO)
        dialects of Lucerne (LU)
        dialects of Zug (ZG)
        dialects of Schwyz (SZ)
        Highest Alemannic
        
        
        
        • dialects of the Bernese Oberland
          dialects of Glarus (GL)
          dialects of Unterwalden (UW) and Uri (UR)
          dialects of the German-speaking parts of Fribourg (FR).
          Walliser German in parts of the Valais (VS)
          Walser German: Via the medieval migration of the Walser, Highest Alemannic was spread to pockets of what are now parts of northern Italy (P), the north west of Ticino (T), parts of Graubünden (GR), Liechtenstein and Vorarlberg. Variation and Distribution
          Note: This page or section contains IPA phonetic symbols in Unicode. See International Phonetic Alphabet for a pronunciation key.
          As Alemannic dialects, Swiss German dialects did not participate in the second German vowel shift during medieval times - they use mostly the same vowels as Middle High German. As such, even though the Alemannic dialects belong to High German, their vowels are closer to Low Saxon than other High German dialects or standard German. An exception are certain central Swiss dialects, e.g. the Uri dialect.
          Examples:
          Most Swiss German dialects, being High-Alemannic dialects, have completed the High German consonant shift, that is, they have not only changed t to [t͡s] or [s] and p to [p͡f] or [f] but also k to [k͡x] or [x]. Most Swiss dialects have initial [x] or [k͡x] instead of k; there are however exceptions, namely the idioms of Chur and Basel. Basel German is a Low Alemannic dialect (like most, but not all, Alemannic dialects spoken in Germany), and Chur German is basically High Alemannic without initial [x] or [k͡x].
          Examples:
          
          History
          
          Consonants
          Most Swiss German dialects have rounded front vowels, unlike many German dialects. Only in the Low Alemannic dialects of northwest Switzerland (mainly Basel) and in the Walliser dialects, these have been unrounded. Due to influence from other Swiss German dialects, the rounding is spreading.
          Like Bavarian dialects, Swiss German dialects have preserved the opening diphthongs of Middle High German: /iə̯, uə̯, yə̯/, e.g. in /liə̯b̥/ 'lovely' (standard German lieb, but pronounced /liːp/); /huə̯t/ 'hat' (standard German Hut /huːt/); /xyə̯l/ 'cool' (standard German kühl /kyːl/). Note that some of those diphthongs have been unrounded in several dialects.
          Like Low Saxon dialects, Swiss German dialects have preserved the old monophthongs /iː, uː, yː/, e.g. /pfiːl/ 'arrow' (standard German Pfeil /pfaɪ̯l/); /b̥uːx/ 'belly' (standard German Bauch /baʊ̯x/); /z̥yːlə/ 'pillar' (standard German Säule /zɔʏ̯lə/).
          Western Swiss German dialects (e.g. Bernese German) have preserved the old diphthongs /ei̯, ou̯/, whereas the other dialects have /ai̯, au̯/ like Standard German.
          
          Vowels
          In many Swiss German dialects, consonant length and vowel length are independent from each other, whereas they interdepend in the other Germanic languages. Examples from Bernese German:
          Stress is more often on the first syllable than in standard German, even in French loans such as [ˈmɛrsːi] or [ˈmersːi] "thanks". Note that there are many different stress patterns even within dialects. Bernese German is one of the dialects where many words are stressed on the first syllable, e.g. [ˈkaz̥ino] 'casino', whereas standard German has [kʰaˈziːno]. However, no Swiss German dialect is as consistent as the Icelandic language in this respect.
          
          Suprasegmentals
          The grammar of Swiss dialects has some specialties compared to Standard German:
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          

          example:	Si	chunt	üse	Chrischtboum	cho	schmücke.
          literal translation:	she	comes	our	Christmas tree	come	adorn
          translation	She comes to adorn our Christmas tree.

          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          

          example:	Si	lat	ne	nid	la	schlafe.
          literal translation:	she	lets	him	not	let	sleep
          translation:	She doesn't let him sleep.

          
          
          This is probably a generalisation of a close association of these verbs with the following verb in perfect tense or modal verb constructions:
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          

          perfect tense:	Si	het	ne	nid	la schlafe.
          literal translation:	she	has	him	not	let sleep
          translation:	She hasn't let/didn't let him sleep.

          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          
          

          modal verb:	Si	wot	ne	nid	la schlafe.
          literal translation:	she	wants	him	not	let sleep
          translation:	She doesn't want to let him sleep.

          
          
          
          There is no preterite indicative (yet there is a preterite subjunctive).
          There is no genitive case, though certain dialects have preserved a possessive genitive (for instance in rural Bernese German).
          The order within verb groups may vary, e.g. wil du bisch cho/wil du cho bisch vs. standard German weil du gekommen bist "because you have come/came".
          All relative clauses are introduced by the relative particle wo ('where'), never by the demonstrative particles der, die, das, welcher, welches as in Standard German, e.g. ds Bispil, wo si schrybt vs. Standard German das Beispiel, das sie schreibt ('the example that she writes'); ds Bispil, wo si dra dänkt vs. Standard German das Beispiel, an das sie denkt ('the example that she thinks of').
          In combinations with other verbs, the verbs gah or goh "go", cho "come", la or lo "let" and aafa or aafo "begin" reduplicate, prefixed to the main verb. Grammar
          The vocabulary is rather rich - especially in rural areas there are many special terms retained, e.g. regarding cattle or weather. In the cities, much of the rural vocabulary has been lost.
          Most borrowings come from Standard German. Many of these are now so common that they have totally replaced the original Swiss German words, e.g. the words Hügel 'hill' (instead of Egg, Bühl), Lippe 'lip' (instead of Lefzge). Others have replaced the original words only in parts of Switzerland, e.g. Butter 'butter' (originally called Anken in most parts of Switzerland). Virtually any Swiss Standard German word can be borrowed into Swiss German, always adapted to Swiss German phonology. However, certain Standard German words are never used in Swiss German, for instance Frühstück 'breakfast', niedlich 'cute' or zu hause 'at home'; instead, the native words Zmorge, härzig and dehei are used.
          Swiss dialects have quite a few words from French, which are perfectly assimilated. Glace (ice cream) for example is pronounced /glas/ in French but [ˈɡ̊lasːeː] or [ˈɡ̊lasːə] in many Swiss German dialects. The French word for 'thank you', merci, is also used as in merci vilmal, literally "thanks many times". Maybe these words aren't direct borrowings from French but survivors of the once more numerous French loans in Standard German, many of which have fallen out of use in Germany.
          In recent years, Swiss dialects have also borrowed some English words which already sound very Swiss, e.g. [ˈfuːd̥ə] ('to eat', from "food"), [ɡ̊ei̯mə] ('to play computer games', from "game") or [ˈz̥nœːb̥ə] - ('to snowboard', from "snowboard"). These words are probably not direct loans from English, but have been adopted through standard German intermediation. While most of those loanwords are of recent origin, some have been in use for decades, e.g. [ˈʃutːə] (to play football, from "shoot").
          There are also a few English words which are modern borrowings from the Swiss German languages. The dishes muesli, and rösti have become English words, as did loess (fine grain), flysch (sandstone formation), bivouac, kepi, landamman, kilch, schiffli, and the act of putsching in a political sense.
          
          Literature
          
          Swiss French, Swiss Italian