eSIM/Electronic SIM/Embedded SIM
This is called by many different names. Some say embedded SIM, some say Electronic SIM and other say eSIM. There would be other names coming out until the industry standard is finalized and adopted widely in the area. Whatever we call, the fundamental idea of this SIM is to distribute the SIM (UICC) as a non-removable/fixed component of a user device (e.g, M2M terminal, Mobile Phone etc). The device manufacturer program the SIM card to load different set of informations required by specific situation (e.g, location, network operator etc)
I will call this as eSIM throughout this page since 'e' can imply many different things(e.g, it can imply 'Electronic', 'Embedded' and even 'Enhanced').
Why eSIM ?
For some people especially who is working on modem development and device testing, it would sound like counter-intuitive evolution path because 'anything fixed/non-removable' may imply 'less flexibility and less controllability'. Then how come this kind of concept is getting more and more frequently talked about (as of Aug 2015).
In engineering, for anything coming out anew, there is some reason/motivation. What is the reason/motivation for this new concept of SIM ?
I think the biggest motivation is related to M2M/IoT devices.
In short, Anyway there seem to be many reasons for moving towards eSIM cards
Is it going to be used only for M2M device ? It doesn't seem to be restricted to M2M/IoT device only and there seems to be some trends towards adopting this technology to mobile phone as well. Read following articles.
How to program (provision) the SIM ?
Now the question is how you can load information (profile) into each eSIM card within the device ? The simplest idea is to implement a special programming port directly connected to the eSIM and electrically load the information into it, but the ideal (final goal) would be to load the information (profile) over the air (this is called 'Remote Provisioning').
The critical issues is how to design/implement a remote provisioning. Since this remote provisioning should be applicable to devices from various vendors and applicable to different network operators, there should be some international standard and very detailed procedures (protocols) should be defined. For now, GSMA is leading this activity. Even though the specification is not finalized yet (as of Aug 2015), you can have pretty detailed idea of Remote Provisioning process from GSMA document : Embedded SIM Remote Provisioning Architecture (Visit Reference  to find the document)
eUICC Architecture/Information Flow
Following is overall Architecture and Information flow modified from GSMA Technical Specification. (I just a couple of items below the dotted line. Everything above the dotted line is exactly same as in GSMA Technical Specification : Figure 1 in GSMA-Embedded-SIM-Remote-Provisioning-Architecture-Version-1.1).
Probably the most of the readers including myself are not very familiar with each of these entities for now (Aug 2015) and inter-relations of each of these entities are also quite complicated. Most of the people would be interested (or involved) in only a couple of path shown here. I will just keep updating the descriptions of possible path combinations (interactions) among these entities as I learn along.
< Path Example 1 : (1), (2), (3) >
Probably this can be a kind of minimum functional flow.
First, SM-DP should get the necessary tools or services from EUM (eUICC Manufacturer) that is required to program the eUICC.
Next, SM-DP should get input data from MNO (Mobile Network Operator) that will be used to create a Profile (or Many Profiles) for the target eUICC. Some examples of the input data are as follows.
How SM-SR communicate to eUICC ?
How SM-SR can communicate to eUICC ? This is the point that I am personally most interested in (You may be more interested in other parts). This communication is supposed to be over-the-air ? Then you might ask 'what kind of OTA technology' and which specific Radio message will be used to carry these information.
I think this should be determined by each MNO and each MNO would use different technology. GSMA Specification mentions of some of possibile mechanism as follows. (In Ref , the section A.2 MNO-SM-DP Interface describes as follows).
All relavant known information on the Target eUICC and its SM-SR e.g:
Once this OTA mechanism is determined, the higher level protocol is relatively clearly defined in the following sections in following sections of Ref 
What is in a Profile ?
A Profile is a set of UICC parameters that is required to attach a Network and perform various functions that the device subscribes. There are roughly three Categories of informaton as follows. (Based on the section 3.4.1 of GSMA Specification (Ref ))
i) Authentication/Security Algorithm Parameters : Algorithms would be Milenage in most of the live network. or it can be 3GPP Test algorithm if it is configured for test. The parameters would be as follows.
ii) Policy Rules attached to the Profile
iii) Other UICC Parameters described TS 31.102 (Many of these parameters might be related to Policy Rules)
Common Use Case
As of now (Sep 2015), there is no international standard about eUICC Profile update method that is commonly adopted even though there are some cases where eUICC are used in terms of hardware. So, the use model listed here would be a kind of idea level.
Case 1 : eSIM is embedded in the device and IMEI (device ID) & ICCID (UICC Serial Number) is informed to end user (or a specific Service Center). And then, the end user (or Service Center) can ask Network Operator (MNO) to activate of eUICC.
 TS 31.102 Characteristics of the Universal Subscriber Identity Module (USIM) application : This documents describes all the parameters and format of UICC parameters.
 TS 31.103 Characteristics of the IP Multimedia Services Identity Module (ISIM) application : Format is similar to 31.102, but it carries information/parameters about IMS Service