# Blockchain: Current Challenges and Future Prospects/Applications
## 2 The Unique Value of Blockchain
### Permissioned vs. Permissionless  
According to the requirements of each deployment of a distributed ledger system, different levels of access permission can be defined. Thus, in general, distributed ledgers can be classified according to the permissions of participation and access control. Mainly these are of two types: (i) _permissionless_; there are no requirements for who joins the network, and there is an open participation policy in place which means anyone can join--in other words, anyone can be a node and participate in the validation process (public networks such as Bitcoin)--and, (ii) _permissioned_; such systems usually operate under the authority of an entity or a consortium. In addition, there is a strict policy on who joins the network and control over the nodes that are participating in the consensus (private or consortium networks built with Hyperledger Fabric). It is often the case that the identity of such nodes is known. Overall, there is great interest in the technologies behind distributed ledger systems that has triggered a significant body of research work on the various consensus protocols according to the requirements and access policies. Furthermore, the unique characteristics of such systems have inspired the development of many interesting applications across the spectrum of many industries. Practically all Industries will be Affected by Blockchain with Three Facing the Highest Disruptive Potential  
Given its advantages, blockchain technology can disrupt practically all industries [13]. At present, startups from a wide spectrum of industries are emerging by developing and monetizing blockchain-based technologies with the aim of disrupting existing business practices or processes [14]. The funds invested in blockchain friendly startups are vast, with total venture capital investments reaching $822 million, from 279 separate VC deals, during the first half of 2019. Interestingly, 159 of the 279 deals were seed stage ones (indicating that the entrepreneurial zeal has not declined), while the remaining ones were no longer building proofs of concepts for the industry, but rather providing workable applications [15] to customers. Today, there are more than 50 leading blockchain startups whose sole purpose is the disruption of traditional industries through the application of blockchain innovations [14]. These startups are in addition to the giant tech firms (Microsoft, IBM, and Alibaba) that are heavily investing in blockchain applications. A recent IDC study [16] estimates worldwide spending on blockchain solutions to reach $15.9 billion by 2023. Global blockchain spending will be led by the banking industry, which will account for roughly 30% of the worldwide total, followed by healthcare, insurance, finance/fintech, and food. In addition, governments can benefit greatly by using blockchain technologies in most of the functions and services they provide to their citizens, reducing costs substantially and improving their efficiency [17]. A notable example is Estonia, where the early adoption of the technology has shown significant prospects. Approximately 99% of public services are available on-line 24/7, and more than 1400 years' worth of time resources have been saved by shifting to digital technologies. For instance, Guardtime [[https://guardtime.com/](https://guardtime.com/)]([https://guardtime.com/](https://guardtime.com/)) uses blockchain technology and includes, among other applications, the health records of all its citizens, allowing them to use any health service they need anywhere in the country. Most importantly, by simply using their ID card they can receive access to their health records in real-time in order to be consulted by the medical personnel examining them, while the system automatically updates its records with the additional information obtained from new examinations.